JP2004264521A - Image forming method and image forming apparatus - Google Patents

Abstract

Provided is an image forming method capable of preventing both reverse transfer and pre-transfer at the same time while preventing cost increase without requiring extra energy or the like, thereby preventing image quality deterioration.
A primary transfer step of temporarily transferring a toner image formed on a latent image carrier to an intermediate transfer member, and transferring the toner image transferred to the intermediate transfer member by the primary transfer to a recording medium. When the toner image is superimposed and transferred onto the intermediate transfer body by combining the next transfer step, an image forming method capable of collectively transferring the superimposed transferred toner image onto the recording medium by a secondary transfer step The step of removing the surface potential of the latent image carrier before executing the primary transfer step of the toner image onto the intermediate transfer body; and the step of contacting the intermediate transfer body and the latent image carrier with the primary A step of controlling the surface potential of the intermediate transfer body so that the toner on the latent image carrier does not transfer to the intermediate transfer body before the transfer step is performed.
[Selection diagram] FIG.

Description

【００９６】
表１の結果から、平均円形度が０．９４以上のものであれば、逆転写はそれ以下のものに比べて格段によくなっており、望ましいトナーの形状として、平均円形度の値が０．９４以上ということが導かれる。
【００９７】
逆転写防止に用いられた除電は中間転写体を対象としても行われるようになっており、その構成を以下に説明する。
通常、タンデム方式の画像形成装置においては、転写工程が複数存在するため、転写を終えて転写位置から下流に移動したベルト部分は転写時に受けた電荷で帯電しており、このまま次回のトナー像の転写を行うと、前回の転写帯電の影響により転写性能が損なわれることがある。
特に高抵抗ベルトの場合、自己除電が困難であるので、除電手段の必要性は高い。このような観点から、本実施形態では図２に示すように、中間転写体除電手段としてのコロトロン１０２が設けられている。
【００９８】
コロトロン１０２に対向する駆動ローラとしての支持ローラ１５を用いて、ＤＣにＡＣを重畳し、ＡＣバイアス５．８［ｋＶ］、ＤＣバイアス６００［Ｖ］で除電したところ、良好な結果が得られた。ＡＣバイアスの「Ｐｅａｋ ｔｏ Ｐｅａｋ」電圧がある値以上になると帯電電位は飽和し、その飽和電位はＤＣ成分とほぼ一致するため、均一でかつ制御性のよい除電が可能となる。
対向部材として駆動ローラ１５を用いなくとも、他の対向部材を設置することで他の場所でもコロトロン１０２を設置可能である。コロトロン１０２の設置位置は、望ましくは、中間転写体クリーニング装置１７の後、且つ転写部最上流部位（図１で示した構成ではイエロー画像に対応する画像形成手段の上流側）がよい。コロトロン１０２は中間転写体１０の裏面側に設けてもよい。
【００９９】
潜像担持体除電手段１０１および中間転写体除電手段（図２において符号１０２で示す部材）に関しては、次の構成を採用することも可能である。
図１，２に示した実施形態では、潜像担持体除電手段としてＬＥＤやＬＤ、キセノンランプなどの光照射デバイスを用いたが、感光体上の電位の高い部分にイオンを照射して除電する方式もある。例えば、コロトロンなどを使用して、ＡＣバイアスなどを印加して正負のイオンを作り出し、非画像部領域に正イオンを供給することで除電することが可能である。この構成では、トナーの付着している画像部領域に対して非画像部領域の電位が高いため、発生したイオンが選択的に非画像部に吸着され、除電される。
また、スコロトロンなどを使用して、トナーの付着した画像部電位と同極性で、且つ絶対値を少し高めにグリッド電位を設定し、トナーと極性の反対のイオンを発生させて除電することも可能である。
【０１００】
図１，２に示した実施形態では、中間転写体除電手段としてコロトロン１０２を用いたが、導電繊維を刷毛状に束ねた固定ブラシを用いてもよい。
【０１０１】
あるいは図８に示すように、例えば導電性繊維を布に植毛したものを導電性のローラにロール状に巻いた回転ブラシ８２を用いてもよい。
いずれも図示しない電源によりブラシに０．５〜２［ｋＶ］程度の直流電圧を印加して、その先端を中間転写ベルト１０に接触させる。
先端部では中間転写ベルト１０との摩擦による電荷の発生や、電荷注入、あるいは微少領域における放電により、電子、イオンの移動が起こり、中間転写ベルト１０が除電される。
【０１０２】
図９に示すように、導電性のブレード８３に図示しない電源により電圧を印加する構成としてもよい。
【０１０３】
中間転写体除電手段として、導電性のローラに電圧を印加する構成としてもよい。ローラを用いる場合には、導電性のゴムローラに電圧を印加し、中間転写ベルト１０に押し付けて除電を行う。基本的には微少空隙での放電による電荷移動であり、ＤＣバイアス印加方式、ＡＣ重畳方式のどちらでも可能である。望ましくは、均一帯電が比較的容易なＡＣ重畳方式がよい。
【０１０４】
以上、接触式の中間転写体除電方式について述べたが、中間転写体除電手段を中間転写体１０に対して非接触状態に保持するようにしてもよい。この場合、中間転写体除電手段が中間転写体１０上のトナー等の異物によって汚染されないので、汚れによる経時的な帯電性能の低下を抑制でき、中間転写体除電機能の高品質を得ることができるとともに、中間転写体除電手段の耐久性の向上を図ることができる。
【０１０５】
例えば図１０に示すように、導電性ローラ８４の端部（中間転写体１０の非画像領域に対応する部分）の外周面に、間隔保持部材としての例えば厚みが均一な粘着層付き樹脂テープ８５を周方向に貼り、中間転写体１０との間に空隙ｇを保持するようにする。この場合、空隙ｇ分だけ除電電位は低下するので、樹脂テープ８５の厚みは８５［μｍ］程度までが望ましい。
また、中間転写体除電手段としてローラを用いる場合には、中間転写体１０と等速で駆動し、中間転写体１０に対する摩擦を極力少なくするようにすることが望ましい。つまり、図１１に示すように、鋸歯状の放電針８６を中間転写体１０に非接触状態に設け、図示しない電源により電圧を印加する構成としてもよい。
【０１０６】
回転ブラシ８２、ブレード８３、導電性ローラ８４、放電針８６等の中間転写体除電手段は、中間転写体１０の裏面側に設けてもよい。このようにした場合、中間転写体１０の内側スペースを利用できるので、構成のコンパクト化を図ることができる。また、中間転写体除電手段として上記導電性ローラ８４等のようにローラを用いる場合には、該ローラを中間転写体１０の支持ローラを兼ねるように設けてもよい。
【０１０７】
本実施形態では、トナーチリの発生を抑制する方法として、上述した中間転写体の抵抗特性に加えて、１次転写行程が実行される前に潜像担持体上のトナーが中間転写体側に転移しない状態に中間転写体の表面電位を制御するようになっており、詳しくは、中間転写体側から潜像担持体側にトナーが引き付けられるバイアス、つまり転写バイアスとは逆の電界を形成するカウンタバイアスを印加して表面電位を制御するようになっている。以下、カウンタバイアスについて説明する。
図１２乃至１７は転写ニップ入り口部で発生するプレ転写による転写チリを抑えるための方式を説明するための模式図である。
トナー帯電極性が負の場合、反転現像を用いるシステムでは、感光体の帯電電位も負であり、光露光によって潜像として記録された画像部は露光によって完全に電位が消失せずに残留電位として−５０〜−７０［Ｖ］程度の電位が残る。この部分に負極性のトナーが現像されるので、画像部は現像後−１５０〜−２５０［Ｖ］程度になる（ただし、現像されるトナーの帯電量と重量による）。
これに対して転写ニップの入り口部付近で中間転写体の表面電位は、システムにもよるが転写のための正極性バイアスが漏洩してきており、比較的良好な条件では、０［Ｖ］、条件が悪い場合においては＋５００［Ｖ］程度になることもある。
【０１０８】
感光体上の画像部電位と、中間転写体の表面電位との関係から、発生する電界は図１２に示すように、トナーが感光体から中間転写体へ移動する側であり、この電界によってトナーは転写前に飛翔しチリとなる。
そこで、図１３に示すように、トナーが感光体から中間転写体に向けて転移する電界が発生しないよう、感光体上の画像部電位よりも転写ニップ前の中間転写体表面電位が低くするように表面電位を制御することにより、図１４に示すように、図１２に示した場合に対して電界の方向は逆になり、トナーを感光体に押し付ける（引き付けさせる）方向に作用しチリが発生しない。なお、図１３では、表面電位の制御、つまり、カウンタバイアスを印加する構成として電圧を印加される導電性のブレード（便宜上、図１３において符号１５０で示す、その名称がカウンタバイアスブレードと称されている）を用いた構成が示されている。
【０１０９】
このようなカウンタバイアス転写法の原理を用いて、中間転写ベルトの表面電位を制御するには、何らかの手段によって直接中間転写体表面に電圧を印加して制御する方法と、転写ニップに進入する前に中間転写体表面を所定電位に帯電させることで制御する方法とに大別される。
前者の方式では、例えば、図１４に示すように、中間転写体として中間転写ベルトを使用し、転写ニップ入り口背面付近に導電性部材であるローラ（便宜上、図１３に示したブレードと同じ機能を有する部材として符号１５０’で示す）を従動可能なように接触して設置し、そのローラにバイアスを印加することによって中間転写ベルト表面まで電圧を誘起させる方法がある。最も簡単で、ローラが中間転写体と等速で移動（従動）可能であり、中間転写ベルト裏面を傷つける心配がないので使いやすい方式であるが、ローラ形状を取る場合にはローラ径はある程度以上は細くできないので、それなりの場所を占有してしまう。
転写させるためには、転写ニップ出口付近で転写バイアスを与える導電性部材を設置する必要があるが、この部材と干渉しないようにしなければならないという欠点も有する。
そこで、板状の導電性部材、例えば、厚さ０．１［ｍｍ］から０．５［ｍｍ］程度のＳＵＳの板（先端は傷つけ防止のためにヤスリなどによって丸めてあることが望ましい）や、導電性ゴムや導電性樹脂の板を固定して設置し、その部材にバイアスを印加することによって同等の効果を得ることができる。この場合、ローラと異なり、転写ニップぎりぎりまで板状部材を設定することができるので効果も大きく、低コストであり、スペースにも余裕が生まれる。
【０１１０】
金属以外に使用する導電性ゴム、樹脂の素材としては、ポリウレタン、ポリウレア、シリコン、ＮＢＲ、ＣＲ、フッ素ゴム、フッ素系樹脂、ポリカーボネイト、ナイロン、ポリプロピレン、ポリエチレンなどにカーボンや金属微粉末のなどの導電性フィラーを分散させて導電特性をもたせたものがある。また、それ自身がイオン導電性を持つ、エピクロロヒドリンゴム等もある。これらの板状の部材は固定され中間転写ベルト裏面に常に接触するので機械的強度があり、且つ摩擦係数が低いものが望ましい。そのため、フッ素系材料などが望ましく、そうでなければ接触部に低摩擦化のための処理を施すなどするとよい。
このような処理を施しても、固定部材として、常に中間転写ベルト裏面と接触するために、異物などを挟み込んだ場合や経時によってベルト裏面が傷ついてしまう可能性がある。このような問題には、導電性ブラシを用いることで改善可能であり、さらに省スペースでもある。
【０１１１】
しかし、この場合にも、ブラシの毛が抜ける可能性があるなど、どの方式も特徴があるので、場合に応じて選択するようにするのがよい。
【０１１２】
もうひとつの中間転写体の表面電位を制御する方法として用いられる、中間転写体の表面を帯電する方法としては、図１５に示すように、コロナチャージャー等によって帯電する方式が代表的である。この場合、スコロトロン方式のチャージャー（便宜上、図１５において符号１５０Ａで示す）を使用して電位を所定の値に調整することが望ましい。
近年はチャージャー系の帯電器はオゾンが発生するということで敬遠される向きもあるが、これに代わるデバイスとして、図１６に示すように、接触ローラ帯電部材（便宜上、図１６において符号１５０Ｂで示す）が挙げられる。この場合、中間転写ベルト表面を負極性に帯電したいのでローラへの印加バイアスも負極性である。トナーも負極性であるのでローラ部材にトナーが吸着する心配もないが、静電的な吸着の怖れがなくともローラと中間転写ベルトの表面に線速差が発生したときなどはどうしても像が乱れてしまう。
そこで、図１７に示すように、中間転写ベルトからわずかに非接触に設置した導電性部材（便宜上、図１７において符号１５０Ｃで示す）に電圧を印加して帯電する、非接触帯電方式も考えられる。
例えば、ＳＵＳの芯金の上に導電性ＮＢＲ被膜（体積抵抗１０^７［Ωｃｍ］）してあるローラの端部に非接触状態を保つためのギャップテープが５０［μｍ］の厚みで巻かれたもので、このテープ部分を非帯電部材に押し付けてバイアスを印加することで非接触に帯電することができ、カラー作像時に中間転写ベルトに載っているトナーと帯電部材が接触することなく帯電させることが可能である。図１５乃至図１７に示した方式は使用条件などを考慮して選択することができる。
【０１１３】
上述した構成・方式によって、画像を良好に保ったまま、すなわち、トナーチリの発生を高精度に抑制したまま、逆転写の発生を高精度に抑えることできるようになった。
このため、逆転写による廃トナーの混色の問題が解決できるようになった。そこで、感光体１つにつき１色の現像装置を備えた、いわゆるタンデム型中間転写式画像形成装置では、感光体クリーニング装置６３に回収される廃トナーは、その感光体で現像された色のトナーがほとんどとなり、トナーを再び現像装置６１に戻して再利用しても、色味が変化するなどの画質上の問題が無くなり、トナーリサイクルが可能となった。これにより廃トナーの排出量を大幅に低減できるとともに、環境負荷を低減でき、ユーザーにおいてもコスト手間の削減などのメリットが生じる。
但し、逆転写トナーがなくとも、１つの感光体に複数個の現像装置を備える、いわゆる１ドラムタイプの画像形成装置（後述）では、感光体が１つであるため、各色の作像時に感光体上に残った転写残トナーが１つのクリーニング装置に回収されてしまい、それぞれの色が混色されるため再利用することが難しくなる。すなわち、上述したトナーリサイクル手段８０が有効に使用できるのは実質的にタンデムタイプに限られる。
【０１１４】
次に、図１８に基づいて、１つの感光体に複数個の現像装置を備えた、いわゆる１ドラムタイプのカラー画像形成装置への適用例を説明する。
本実施形態における画像形成装置としてのカラー複写機において、露光手段としての書き込み光学ユニット４００は、カラースキャナ２００からのカラー画像データを光信号に変換して原稿画像に対応した光書き込みを行い、潜像担持体である感光体ドラム４０２上に静電潜像を形成する。
【０１１５】
該書き込み光学ユニット４００は、レーザーダイオード４０４、ポリゴンミラー４０６とその回転用モータ４０８、ｆ／θレンズ４１０や反射ミラー４１２等により構成されている。
感光体ドラム４０２は、矢印で示すように反時計回りの向きに回転され、その周囲には、感光体クリーニングユニット４１４、除電ランプ４１６、電位センサ４２０、回転式現像装置４２２のうちの選択された現像器（図１５では現像器４３８）、現像濃度パターン検知器４２４、潜像担持体除電手段４２５、中間転写体としての中間転写ベルト４２６等が配置されている。中間転写ベルト４２６は、第１の実施形態における中間転写体１０と同様の高抵抗ベルトである。
【０１１６】
回転式現像装置４２２は、ブラック用現像器４２８、シアン用現像器４３０、マゼンタ用現像器４３２、イエロー用現像器４３４と、各現像器を回転させる図示しない回転駆動部を有している。
待機状態では、回転式現像装置４２２は、ブラック現像の位置にセットされており、コピー動作が開始されると、カラースキャナ２００で所定のタイミングからブラック画像のデータの読み取りがスタートし、この画像データに基づいてレーザ光による光書き込み・静電潜像（ブラック潜像）の形成が始まる。
【０１１７】
このブラック潜像の先端部から現像するために、ブラック用現像器４２８の現像位置に潜像先端部が到達する前に、現像スリーブを回転開始してブラック潜像をブラックトナーで現像する。感光体ドラム４０２にはマイナス極性のトナーが作像される。
そして、以後、ブラック潜像領域の現像動作を続けるが、潜像後端部がブラック現像位置を通過した時点で、速やかにブラックのための現像位置から次の色の現像位置まで、回転式現像装置４２２が回転する。当該動作は、少なくとも、次の画像データによる潜像先端部が到達する前に完了させる。
【０１１８】
像形成サイクルが開始されると、まず、感光体ドラム４０２は矢印で示すように反時計回りの向きに、中間転写ベルト４２６は時計回りの向きに、図示しない駆動モータによって回転させられる。中間転写ベルト４２６の回転に伴って、ブラックトナー像形成、シアントナー像形成、マゼンタトナー像形成、イエロートナー像形成が行われ、最終的にブラック（Ｂｋ）、シアン（Ｃ）、マゼンタ（Ｍ）、イエロー（Ｙ）の順に、中間転写ベルト４２６上に重ねられ（１次転写）、トナー像が形成される。
図１，２に示した実施形態と同様に、各トナー像の現像工程の後、且つ、中間転写体４２６への転写工程の前に潜像担持体除電手段４２５により感光体ドラム４０２の表面の電位が除電される。
【０１１９】
中間転写ベルト４２６は、感光体ドラム４０２に対向する１次転写手段としての１次転写バイアスローラ４５０、駆動ローラ４４４、２次転写ローラ４５４に対向する２次転写対向ローラ４４６、中間転写ベルト４２６の表面を清掃するクリーニング手段４５２に対向するクリーニング対向ローラ４４８Ａの各支持部材間に張架されており、図示しない駆動モータにより駆動制御されるようになっている。
感光体ドラム４０２に順次形成されるブラック、シアン、マゼンタ、イエローの各トナー像が中間転写ベルト４２６上で正確に順次位置合わせされ、これによって４色重ねのベルト転写画像が形成される。このベルト転写画像は２次転写対向ローラ４４６により記録媒体としての用紙に一括転写される。
【０１２０】
給紙バンク４５６内の各記録紙カセット４５８、４６０、４６２には装置本体内のカセット４６４に収容された用紙のサイズとは異なる各種サイズの用紙が収容されており、これらのうち、指定されたサイズ紙の収容カセットから、該指定された用紙が給紙コロ４６６によってレジストローラ対４７０方向に給紙・搬送される。図１８において、符号４６８はＯＨＰ用紙や厚紙等のための手差し給紙トレイを示す。
像形成が開始される時期に、用紙は上記いずれかのカセットの給紙口から給送され、レジストローラ対４７０のニップ部で待機する。そして、２次転写対向ローラ４４６に中間転写ベルト４２６上のトナー像の先端がさしかかるときに、丁度用紙先端がこの像先端に一致するようにレジストローラ対４７０が駆動され、用紙と像のレジスト合わせが行われる。
【０１２１】
このようにして、用紙が中間転写ベルト４２６と重ねられて、トナーと同極性の電圧が印加される２次転写対向ローラ４４６の下を通過する。このとき、トナー画像が用紙に転写される。続いて、用紙は除電され、中間転写ベルト４２６から剥離して紙搬送ベルト４７２に移る。
中間転写ベルト４２６から４色重ねトナー像を一括転写された用紙は、紙搬送ベルト４７２によりベルト定着方式の定着装置４７０へ搬送され、この定着装置４７０で熱と圧力によりトナー像を定着される。定着を終えた用紙は排出ローラ対４８０で機外へ排出され、図示しないトレイにスタックされる。これにより、フルカラーコピーが得られる。
【０１２２】
高抵抗ベルトの特性上、１次転写バイアスローラ４５０による転写バイアスは、感光体ドラム４０２と中間転写ベルト４２６が接触した位置の裏面に直接印加する方式が望ましい。潜像担持体除電手段の変形例、中間転写ベルト４２６の除電構成は、上述したものと同様に実施することができる。図１８には、図１４に於いて用いた符号１５０’によりローラを用いたカウンタバイアス構成が示されている。この構成において、中間転写ベルト４２６を対象として、図１３および図１４に示した原理およびメカニズムによってトナーチリの発生を防ぐようになっている。
【０１２３】
【発明の効果】
請求項１および２０記載の発明によれば、中間転写体へのトナー像の１次転写前に潜像担持体の除電行程を実行すると共に潜像担持体側に担持されているトナーが中間転写体側に転移しない状態に中間転写体の表面電位を制御し、特に請求項２０記載の発明においては、潜像担持体側のトナーと同極性で絶対値がトナーの帯電電位以上となる制御を実行するので、潜像担持体側と中間転写体側との間に形成される電界の方向をトナーが中間転写体側に飛翔しない方向とすることができる。これにより、中間転写体側への塵状トナーの飛翔が抑制されて、潜像担持体に対する除電行程による逆転車の防止とプレ転写によるトナーチリの発生防止との双方を達成することができ、画像品質の劣化を防止することが可能となる。
【０１２４】
請求項２および３記載の発明によれば、中間転写体の裏面での面積抵抗率およびまたは体積抵抗率を所定値に規定することにより、プレ転写を効率よく防止することが可能となる。
【０１２５】
請求項４記載の発明によれば、潜像担持体側での画像部と非画像部との間の電位差を規定することにより、逆転写の防止効率を高めることが可能となる。
【０１２６】
請求項５記載の発明によれば、光照射という簡単な構成により潜像担持体の除電行程を実行することができるので、除電行程を実行するための構成の設置箇所が狭い場合でも確実に除電することができ、画像部と非画像部との間の電位差を既定値に設定することが可能となる。
【０１２７】
請求項６記載の発明によれば、イオンを用いて除電行程を実行することにより、潜像担持体での必要以上の光照射が行われた場合に発生しやすい感光層の光疲労を低減して潜像担持体の長寿命化が可能となる。
【０１２８】
請求項７記載の発明によれば、除電行程の実行時期を規定することにより、現像行程実行後に行われる転写行程時には、潜像担持体側での画像部と非画像部との間の電位差が規定値に設定されていることになり、電位差が大きくなることで発生する逆転車を確実に抑制した状態での１次転写行程の実行が可能となる。
【０１２９】
請求項８記載の発明によれば、除電行程で用いられる停電量が画像の情報に応じた量に規定されるので、潜像担持体側にとって望ましくない光疲労を低減することができ、逆転写防止のためのエネルギーロスを抑えることが可能となる。
【０１３０】
請求項９記載の発明によれば、電荷の蓄積が生じない１色目を除いて２色目以降の画像転写の際に除電行程が実行されるので、逆転写防止のためのエネルギー消費を最少限として、エネルギーロスを低減することが可能となる。
【０１３１】
請求項１０記載の発明によれば、除電行程が中間転写体をも対象として実行できるので、中間転写体に残留した電荷による次の転写行程への悪影響を排除して良好な転写画像を得ることが可能となる。
【０１３２】
請求項１１記載の発明によれば、中間転写体での除電にコロトロン方式を用いることにより所定電位の印加を容易に行うことが可能となる。
【０１３３】
請求項１２記載の発明によれば、中間転写体での除電が、導電性のブラシに電圧を印加する構成を用いて実行されるので、省スペースで且つ摩擦による傷発生を極力防止して電圧を印加することができるので、構成の簡易化と中間転写体の長寿命化を図ることができる。
【０１３４】
請求項１３記載の発明によれば、中間転写体での除電が、導電性のブレードに電圧を印加する構成を用いて実行されるので、中間転写体の裏面にも容易に配置でき、構成の簡易化と中間転写体除電構成のレイアウト上の自由度を向上させることができる。
【０１３５】
請求項１４記載の発明によれば、中間転写体での除電が、導電性のローラに電圧を印加する構成を用いて実行されるので、中間転写体と等速に駆動することにより、中間転写体との摩擦を極力抑制しながら電圧を印加することができ、中間転写体の長寿命化を図ることができる。
【０１３６】
請求項１５記載の発明によれば、中間転写体での除電が、導電性の鋸歯状の放電針に電圧を印加する構成を用いて実行されるので、構成の簡易化と中間転写体の長寿命化を図ることができる。
【０１３７】
請求項１６記載の発明によれば、中間転写体での除電が上記中間転写体に接触して除電する構成を用いて実行されるので、放電によるオゾンの発生量を少なくすることができ、作業環境の安全性の向上を図ることができる。
【０１３８】
請求項１７記載の発明によれば、中間転写体での除電が中間転写体に非接触状態で除電する構成を用いて実行されるので、汚れによる帯電性能の低下を抑制でき、信頼性の高い除電機能を長期に亘って得ることができる。
【０１３９】
請求項１８記載の発明によれば、中間転写体での除電が、中間転写体ヲ用いた２次転写行程後で１次転写行程前に実行されるので、最も効果的な位置で除電を行うことができ、除電効率を向上させることができる。
【０１４０】
請求項１９記載の発明によれば、中間転写体の表面電位制御が、中間転写体の移動方向で潜像担持体と対面する位置の上流側で背面側から電圧印加可能な導電性部材を用いて行われるので、中間転写体表面の転写面での接触などを避けて表面電位を所定条件に設定することができ、トナーチリの発生を招くプレ転写を防止する状態とすることができる。
【０１４１】
請求項２０乃至２３記載の発明によれば、中間転写体の表面電位制御に用いられる導電性部材がその設置条件や環境条件に対応して選択できるので、表面電位制御の際の電圧印加効率を良好な状態にしてプレ転写の発生を防止できる表面電位の設定が可能となる。
【０１４２】
請求項２４記載の発明によれば、帯電方式により表面電位制御を行うことにより、表面電位制御のための電圧印加が背面から行いにくいドラムなどの構成を採用された中間転写体であっても、表面電位を制御してプレ転写の発生を防止することが可能となる。
【０１４３】
請求項２５記載の発明によれば、表面電位制御のための帯電構造としてスコロトロン方式を用いているので、既存の確立された方式を用いて所定の電位を容易に設定することができる。
【０１４４】
請求項２６記載の発明によれば、中間転写体の帯電構造として中間転写体に接触して等速で移動可能な導電性部材を用いて電圧を印加する構成が用いられるので、オゾンなどの放電生成物の発生を防止しながらプレ転写を抑制する表面電位を設定することが可能となる。
【０１４５】
請求項２７記載の発明によれば、中間転写体への帯電構造として中間転写体に非接触な導電性部材を用いて電圧を印加する構成であるので、中間転写体上に担持されている画像に接して乱すようなことなく画質劣化を招くプレ転写を防止できる表面電位を設定することができることになる。
【０１４６】
請求項２８記載の発明によれば、中間転写体の表面電位が潜像担持体に形成される画像の情報に応じて設定されるので、プレ転写の発生時期でない場合には、逆転写に対する最適な条件を設定することにより、逆転写の防止を確実に行えるようにすることができる。
【０１４７】
請求項２９記載の発明によれば、潜像担持体上に形成される画像の情報に応じて、上記中間転写体に印加される転写バイアスを設定するので、転写バイアスの最適化によって逆転写を高精度に防止でき、また、逆転写防止のためのエネルギーロスを最小限に止めることができる。
【０１４８】
請求項３０記載の発明によれば、転写されるトナー像形成に用いられるトナーを、円形度が０．９４以上に設定しているので、逆転写を高精度に抑制することができ、高画質化を一層向上させることができる。
【０１４９】
請求項３１記載の発明によれば、逆転写とプレ転写との双方が防止できることにより、画質劣化のない高画質化を可能にすることができる。
【０１５０】
請求項３２記載の発明によれば、各潜像担持体に対応してそれぞれ、該潜像担持体上の静電潜像をトナー像として可視化する現像手段と、上記中間転写体への転写後に残留したトナーを除去・回収するクリーニング手段が設けられ、上記各潜像担持体のうち少なくとも１つの潜像担持体について、上記クリーニング手段により回収されたトナーを該潜像担持体に対応する上記現像手段へ戻すトナーリサイクル手段が設けられている構成としたので、廃棄トナーの低減化により無駄なトナー消費の抑制、環境負荷の低減に寄与することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る画像形成方法を適用される画像形成装置としてのカラー複写機の概要正面図である。
【図２】画像形成部と中間転写体の拡大図である。
【図３】感光体の画像部と非画像部の表面電位差と逆転写量との関係を示す実験結果のグラフである。
【図４】感光体の非画像部電位とドットチリとの関係を示す実験結果のグラフである。
【図５】中抵抗ベルトを用いた間接バイアス印加転写方式と高抵抗ベルトを用いた間接バイアス印加転写方式とにおけるドットチリとの関係を示す実験結果のグラフである。
【図６】円形度の違いによるトナーと感光体との接触面積の違いを示す図である。
【図７】添加剤を介したトナーと感光体との接触状態を示す図である。
【図８】図２に示した中間転写体の除電行程に用いられる構成の一つを示す図である。
【図９】図２に示した中間転写体の除電行程に用いられる構成の他の一つを示す図である。
【図１０】図２に示した中間転写体の除電行程に用いられる構成の別の一つを示す図である。
【図１１】図２に示した中間転写体の除電行程に用いられる構成のさらに他の一つを示す図である。
【図１２】本発明の実施形態に係る画像形成方法の前提となるトナーチリ発生のメカニズムを説明するための模式図である。
【図１３】本発明の実施形態に係る画像形成方法で用いられるプレ転写防止原理を説明するために中間転写体での表面電位の変化状態を示す模式図である。
【図１４】図１３に示した原理に基づくプレ転写防止メカニズムを説明するための模式図である。
【図１５】図２に示した中間転写体の帯電構造の一つを示す模式図である。
【図１６】図２に示した中間転写体の帯電構造の他の例を示す模式図である。
【図１７】図２に示した中間転写体の帯電構造の別の例を示す模式図である。
【図１８】本発明の実施形形態に係る画像形成方法が適用される画像形成装置の別の例を説明するための図である。
【図１９】プレ転写の発生状態を示す図である。
【図２０】感光体の画像部と非画像部の表面電位差が大きい場合と小さい場合におけるプレ転写の発生状態の差異を示す図である。
【符号の説明】
１０、４２６ 中間転写体
１７ クリーニング手段としての中間転写体クリーニング装置
２２ ２次転写手段としての２次転写装置
４０Ｙ、４０Ｃ、４０Ｍ、４０Ｂｋ、４０２ 潜像担持体としての感光体
６１Ｙ、６１Ｃ、６０Ｍ、６０Ｂｋ 現像手段としての現像装置
６２ １次転写手段としての１次転写ローラ
８０ トナーリサイクル手段
１０１Ｃ、１０１Ｍ、１０１Ｂｋ、４２５ 潜像担持体除電手段
４５４ ２次転写手段としての２次転写ローラ
１５０ 表面電位制御のためのカウンタバイアス手段の一つであるブレード
１５０’ 表面電位制御のためのカウンタバイアス手段の他の一つであるローラ
１５１，１５１Ａ、１５１Ｂ 帯電手段
Ｓ 記録媒体としてのシート[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming method and an image forming apparatus, and more particularly, to a transfer method using a transfer device capable of superimposing and transferring not only a single color image but also a plurality of color images and a configuration thereof.
[0002]
[Prior art]
2. Description of the Related Art A color image forming apparatus capable of forming not only a single color image but also a multi-color image including a full color is known for an image forming apparatus using an electrophotographic method. In recent years, color copying machines and color printers, as well as printing machines and facsimile machines, have been put into practical use.
[0003]
The following configuration is known as a configuration of a color image forming apparatus.
[0004]
In a first configuration, a plurality of developing devices are arranged so as to be able to contact and separate from a drum-shaped photoconductor used as a latent image carrier, and a toner image of each color is formed for each rotation of the photoconductor. There is a so-called one-drum system in which the image is sequentially transferred from a photoconductor to an intermediate transfer member or a transfer material such as paper held on a transfer drum to create a color toner image (for example, Non-Patent Document 1). ).
[0005]
On the other hand, in the case of the one-drum system, the photoreceptor needs to be rotated four times, which is unsuitable for full-color image formation at a speed similar to monochrome, which has been demanded in recent years. For this reason, the number of photoconductors is increased by the number of colors (usually three or four), the photoconductors are juxtaposed, and respective developing devices are arranged corresponding to the photoconductors, and the developed toner images of the respective colors are formed. A configuration in which primary transfer is superimposed on an intermediate transfer member, and a transfer image is collectively transferred on a transfer material such as paper by secondary transfer, or each color is sequentially transferred while moving the transfer material to a transfer position of each photosensitive member. There is a tandem system or an in-line system using a configuration for superimposing and transferring the toner image (for example, Non-Patent Document 2).
[0006]
A common problem in any of the color image forming apparatuses using any of the methods is that the toner image transferred to the transfer member is transferred to the photosensitive member, which is a latent image carrier, and so-called reverse transfer occurs. is there.
[0007]
The reverse transfer phenomenon occurs when a transfer bias voltage is applied to an image forming unit located on the downstream side in the moving direction of the intermediate transfer body to be superimposedly transferred, and the toner image on the image carrier is moved to the intermediate transfer body. In particular, reverse transfer occurs in the non-image area of the image carrier.
[0008]
The mechanism by which reverse transcription occurs is considered as follows.
In the case of an image forming apparatus using a negative / positive reversal developing method in which a toner image having the same polarity as the latent image carrier is attached to obtain a toner image, the surface of the latent image carrier is charged to the same polarity as the toner by a charging unit. I have. On the other hand, the surface potential of the intermediate transfer member has a polarity opposite to that of the toner, or 0 [V].
[0009]
If the potential difference between the latent image carrier and the surface of the intermediate transfer member is large, particularly in the non-image area of the latent image carrier, the potential difference is further increased. The charged polarity of a part of the toner carried on the intermediate transfer member is inverted by the ionized ions generated at this time.
[0010]
As a result, the toner whose polarity has been inverted in the primary transfer portion receives an electrostatic attraction toward the latent image carrier and moves to the latent image carrier.
[0011]
Conventionally, as a configuration for preventing the reverse transfer phenomenon, an optical static eliminator is installed at a position immediately before the toner image on the latent image carrier is transferred onto the intermediate transfer member, and the latent image before the transfer process after the development process is provided. There has been proposed a configuration using measures to reduce the potential difference between the latent image carrier and the intermediate transfer body by eliminating the charge on the surface of the carrier, thereby suppressing discharge and reducing reverse transfer (for example, see Patent Document 1). 1, Patent Document 2).
As another configuration, after the development step, before the transfer step, a static eliminator is provided to eliminate the charge on the surface of the latent image carrier, and the potential difference between the latent image carrier surface and the intermediate transfer member surface is determined by forming an image on each image forming unit. There has been proposed a configuration in which a control unit that performs control based on a situation is installed (for example, Patent Document 3).
There has also been proposed a configuration in which toner adhering force to an image portion is increased separately from a potential difference between an image portion and a non-image portion on the surface of the latent image carrier (for example, Patent Document 4).
[0012]
[Non-patent document 1]
The Society of Electrophotography, "Continuing Basics and Applications of Electrophotographic Technology" (November 15, 1996, First Edition, First Edition, p34, Figure 1.23)
[Non-patent document 2]
The Society of Electrophotography, "Continuing Basics and Applications of Electrophotographic Technology" (November 15, 1996, First Edition, First Edition, p36, Fig. 1.25)
[Patent Document 1]
JP-A-5-165383 (paragraph "0021" column)
[Patent Document 2]
JP-A-9-90705 (paragraph "0034" column)
[Patent Document 3]
JP-A-2001-125399 (paragraph "0062" column)
[Patent Document 4]
JP-A-2002-55544 (paragraph "0021" column)
[0013]
[Problems to be solved by the invention]
After the developing step, when the latent image carrier before the transfer step is neutralized by a static elimination means, the potential difference between the latent image carrier and the intermediate transfer body becomes small, and the amount of discharge is small or no discharge. No reverse transfer occurs, but the image quality caused by the potential difference between the image area and the non-image area on the latent image carrier is reduced when the latent image carrier is discharged after the development step and before the transfer step. Deterioration occurs.
[0014]
This image quality deterioration occurs due to a phenomenon called “pre-transfer”.
Pre-transfer is a phenomenon in which a transfer electric field for primary transfer is formed before a transfer area with respect to an intermediate transfer member, so that toner moves from a latent image carrier to an intermediate transfer member before transfer. It does not occur on the image carrier.
[0015]
More specifically, as shown in FIG. 19, as the potential difference between the image area and the non-image area of the photoconductor 40 decreases, the attraction force of the toner T onto the photoconductor 40 decreases, and the primary transfer is performed. The toner T scatters and adheres to the non-image area of the intermediate transfer belt 500 before the transfer by the electric field. This results in toner dust, which means that the toner is scattered in the form of dust, resulting in image quality deterioration in which a clear image cannot be obtained.
[0016]
This phenomenon will be described in more detail. As shown in FIG. 20, when the potential difference between the image area and the non-image area on the photoconductor 40 is large, as shown in FIG. By discharging the non-image area with the intermediate transfer belt 500, a latent image (potential well) corresponding to the photoconductor 40 is formed on the intermediate transfer belt 500, and the toner T is pre-transferred by the primary transfer electric field. Even if the non-image area on the intermediate transfer belt 500 does not move, it is forcibly attracted to the formed potential well (image area).
[0017]
Conversely, when the potential difference between the image area and the non-image area on the photoreceptor 40 is small, the potential well is not formed firmly on the intermediate transfer belt 500 as shown in FIG. The boundary between the non-image area and the non-image area becomes ambiguous in terms of electric field, so that the toner T scatters and moves during pre-transfer regardless of the image area and the non-image area.
[0018]
As a result, the image quality deteriorates significantly. In FIG. 20, Vopc indicates the potential of the photoconductor 40, Vtoner indicates the potential of the toner, and Vbelt indicates the potential of the intermediate transfer belt 500.
[0019]
As described above, the countermeasures against reverse transfer and the countermeasures against pre-transfer are in conflict with each other, and it has been difficult to achieve both in a desirable state.
[0020]
It is effective to prevent the pre-transfer caused by the phenomenon in which the dusty toner inadvertently flies by increasing the charge of the toner, as proposed in Patent Document 4, but it is effective to increase the charge of the toner. In order to increase the cost, it is necessary to newly provide a charge applying means for performing the operation, and not only to complicate the configuration but also to use extra energy for applying the charge.
[0021]
SUMMARY OF THE INVENTION In view of the above-described problems in the conventional transfer process, an object of the present invention is to prevent an increase in cost without using extra energy or the like, and to simultaneously prevent both reverse transfer and pre-transfer, thereby preventing image deterioration. An object of the present invention is to provide a forming method and an image forming apparatus.
[0022]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a primary transfer step in which a toner image formed on a latent image carrier is temporarily transferred to an intermediate transfer body, and the toner image transferred to the intermediate transfer body by the primary transfer is recorded on a recording medium. When the toner image is superimposed and transferred onto the intermediate transfer body by combining with the secondary transfer process for transferring the toner image to the recording medium, the superimposed and transferred toner image can be collectively transferred to the recording medium by the secondary transfer process. In the image forming method, the step of removing the surface potential of the latent image carrier before executing the primary transfer process of the toner image to the intermediate transfer body is performed, and the intermediate transfer body and the latent image carrier come into contact with each other. Controlling the surface potential of the intermediate transfer body so that the toner on the latent image carrier does not transfer to the intermediate transfer body side before the primary transfer step is performed. I have.
[0023]
According to a second aspect of the present invention, in addition to the first aspect, the intermediate transfer member has a rear surface with a sheet resistivity of 10%. ⁹ [Ω / □] or more.
[0024]
According to a third aspect of the present invention, in addition to the first aspect, the intermediate transfer member has a volume resistivity of 10%. ^Thirteen [Ωcm] or more.
[0025]
According to a fourth aspect of the present invention, in addition to the first aspect, the potential difference between the image portion and the non-image portion after performing the charge removal process of the latent image carrier and before the primary transfer process is 0 [V] or more. It is characterized in that it is set within 200 [V].
[0026]
According to a fifth aspect of the present invention, in addition to the first aspect of the present invention, light irradiation is used in the neutralization step.
[0027]
The invention according to claim 6 is characterized in that, in addition to the invention according to one of claims 1 to 4, ions generated by an ion generator are used in the charge removal step.
[0028]
According to a seventh aspect of the present invention, in addition to the one of the first to fourth aspects, the execution position of the charge removal step is after the development step for the latent image carrier, and It is characterized by a position corresponding to a position before the next transfer step.
[0029]
According to an eighth aspect of the present invention, in addition to the first aspect of the present invention, in the static elimination step, the static elimination amount is set according to information of an image formed on the latent image carrier. It is characterized by that.
[0030]
According to a ninth aspect of the present invention, in addition to the first aspect of the present invention, in the discharging step, the toner images of the second and subsequent colors when a toner image is superimposed on the intermediate transfer member are formed. It is characterized in that it is executed before transferring.
[0031]
According to a tenth aspect of the present invention, in addition to the one of the first to ninth aspects, the neutralization step can be set for the intermediate transfer body separately from the latent image carrier. That is, the electric charge accumulated in the intermediate transfer member is eliminated.
[0032]
According to an eleventh aspect of the present invention, in addition to the tenth aspect of the present invention, a corotron type static elimination structure is used in the neutralization step for the intermediate transfer member.
[0033]
According to a twelfth aspect of the present invention, in addition to the tenth aspect, a configuration in which a voltage is applied to a conductive brush is used in the neutralization process for the intermediate transfer body.
[0034]
A thirteenth aspect of the present invention is characterized in that, in addition to the tenth aspect, a configuration in which a voltage is applied to a conductive blade is used in the neutralization process for the intermediate transfer body.
[0035]
According to a fourteenth aspect of the present invention, in addition to the tenth aspect, a configuration in which a voltage is applied to a conductive roller is used in the neutralization process for the intermediate transfer body.
[0036]
According to a fifteenth aspect of the present invention, in addition to the tenth aspect, a configuration in which a voltage is applied to a conductive saw-toothed discharge needle is used in the neutralization process for the intermediate transfer body. Features.
[0037]
According to a sixteenth aspect of the present invention, in addition to the one of the tenth to fifteenth aspects, in the neutralization process for the intermediate transfer body, a member used for neutralization contacts the intermediate transfer body. It is characterized by being used after being used.
[0038]
According to a seventeenth aspect of the present invention, in addition to the one of the tenth to fifteenth aspects, in the charge elimination process for the intermediate transfer member, a member used for charge elimination is not attached to the intermediate transfer member. It is characterized in that it is used in a contact state.
[0039]
According to an eighteenth aspect of the present invention, in addition to the one of the tenth to seventeenth aspects, the charge elimination process for the intermediate transfer member is performed after the secondary transfer process and before the primary transfer process. It is characterized by being executed.
[0040]
According to a nineteenth aspect of the present invention, there is provided a primary transfer step of temporarily transferring a toner image formed on a latent image carrier to an intermediate transfer member, and a recording medium for transferring the toner image transferred to the intermediate transfer member by the primary transfer. When the toner image is superimposed and transferred onto the intermediate transfer body by combining with the secondary transfer process for transferring the toner image to the recording medium, the superimposed and transferred toner image can be collectively transferred to the recording medium by the secondary transfer process. In addition to the present invention, the step of removing the surface potential of the latent image carrier before the primary transfer process of the toner image onto the intermediate transfer body is performed, and the intermediate transfer body and the latent image carrier come into contact with each other. Before the primary transfer step is performed, the surface potential of the intermediate transfer body is carried on the latent image carrier so that the toner on the latent image carrier does not transfer to the intermediate transfer body. The polarity is the same as the toner and the absolute value is It is characterized in that the surface potential control of setting the above charge potential is performed.
[0041]
According to a twentieth aspect of the present invention, in addition to the nineteenth aspect, in the surface potential control, an upstream side of the facing position in a direction in which the intermediate transfer body moves toward a position facing the latent image carrier. A conductive member provided in contact with the back surface of the intermediate transfer member on the side, and a voltage is applied to the conductive member.
[0042]
According to a twenty-first aspect of the present invention, in addition to the twentieth aspect, a roller is used as the conductive member.
[0043]
According to a twenty-second aspect of the present invention, in addition to the twentieth aspect, a blade member is used as the conductive member.
[0044]
According to a twenty-third aspect of the present invention, in addition to the twentieth aspect, a brush is used as the conductive member.
[0045]
According to a twenty-fourth aspect of the present invention, in addition to the nineteenth aspect, the surface potential control is performed by charging a surface of the intermediate transfer body facing the latent image carrier. I have.
[0046]
According to a twenty-fifth aspect of the present invention, in addition to the twenty-fourth aspect, a scorotron charging structure is used as the charging structure of the intermediate transfer member.
[0047]
According to a twenty-sixth aspect of the present invention, in addition to the twenty-fourth aspect, as the charging structure of the intermediate transfer body, a conductive structure capable of contacting the intermediate transfer body and moving at a speed equal to the moving speed of the intermediate transfer body. A conductive member is used, and a voltage is applied to the conductive member.
[0048]
According to a twenty-seventh aspect of the present invention, in addition to the twenty-seventh aspect, a conductive member that is not in contact with the intermediate transfer body is used as a charging structure of the intermediate transfer body. , A voltage is applied.
[0049]
According to a twenty-eighth aspect of the present invention, in addition to the first aspect of the invention, the surface potential of the intermediate transfer member is determined based on information of an image formed on the latent image carrier. It is characterized by being set according to.
[0050]
According to a twenty-ninth aspect of the present invention, in addition to the one of the first to third aspects or the nineteenth to twenty-eighth aspects, the transfer bias for the intermediate transfer member is determined by the transfer bias of the image formed on the latent image carrier. It is characterized by being set according to information.
[0051]
According to a thirtieth aspect of the present invention, in addition to the one of the first to twenty-ninth aspects, the circularity is set to 0.94 or more as the toner used for forming the transferred toner image. It is characterized by:
[0052]
The invention according to claim 31 is characterized in that the image forming method according to any one of claims 1 to 30 is used in an image forming apparatus.
[0053]
According to a thirty-second aspect of the present invention, in addition to the thirty-first aspect, a plurality of latent image carriers, a latent image forming means provided for each of the latent image carriers, and a latent image carrier are provided. Developing means for processing the electrostatic latent image formed on the image carrier into a visible image; transferring means for transferring the toner image converted to a visible image by the developing means onto the same transfer medium; Cleaning means for collecting the toner remaining on the image carrier, wherein the toner collected by the cleaning means is returned to the developing means for reuse.
[0054]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an image forming apparatus to which an image forming method according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type using a tandem system, that is, a so-called tandem intermediate transfer type. However, the image forming apparatus according to the present invention is not limited to this, and includes a color printer, a facsimile machine, and a printing machine.
[0055]
In FIG. 1, the color copier includes a copier main body 1, a paper feed table 2 on which the copier main body 1 is mounted, a scanner 300 provided on an upper surface of the copier main body 1, and an upper part of the scanner 3. An automatic document feeder (ADF) 4 is provided.
[0056]
An endless belt-shaped intermediate transfer body (intermediate transfer belt) 10 is disposed in the copying apparatus main body 1 at substantially the center. The intermediate transfer member 10 is supported by being hung around three support rollers 14, 15, and 16, and is driven to rotate clockwise in the figure by a drive source (not shown).
[0057]
In this embodiment, of the three support rollers 14, 15, and 16, an intermediate toner for removing residual toner remaining on the intermediate transfer body 10 after image transfer (secondary transfer) is provided near the second support roller 15. A transfer body cleaning device 17 is provided (see FIG. 2, omitted in FIG. 1).
[0058]
Of the three support rollers 14, 15, 16, yellow (Y) is placed on the intermediate transfer body 10 stretched between the first support roller 14 and the second support roller 15 along the transport direction. , Cyan (C), magenta (M), and black (Bk) are arranged side by side to form a tandem image forming unit 20. However, these four color orders are merely examples, and are not intended to limit the present invention.
[0059]
FIG. 2 is an enlarged view of a part of the tandem image forming unit 20. In the tandem image forming unit 20, in the image forming units 18Y, 18C, 18M, and 18Bk, which are individual toner image forming units, as shown in FIG. 2, drum-shaped photoconductors 40Y, 40C, and 40M as latent image carriers are provided. , 40Bk, charging rollers 60Y, 60C, 60M, 60Bk as charging devices, developing devices 61Y, 61C, 60M, 60Bk, primary transfer rollers 62Y, 62C, 62M, 62Bk as primary transfer devices, and photoconductor cleaning There are provided devices 63Y, 63C, 63M, 63Bk and static eliminators 64Y, 64C, 64M, 64Bk for initializing the surface potential of the photoconductor.
[0060]
In the present embodiment, the charging rollers 60Y, 60C, 60M, and 60Bk are brought into contact with the photoconductors 40Y, 40C, 40M, and 40Bk to apply a voltage to charge the photoconductors 40Y, 40C, 40M, and 40Bk. However, as a matter of course, charging may be performed by a non-contact corotron charger.
[0061]
As shown in FIG. 1, a writing device 21 is disposed above the tandem image forming unit 20. A secondary transfer device 22 is disposed on the side opposite to the tandem image forming unit 20 with respect to the intermediate transfer body 10. The secondary transfer device 22 is configured by wrapping an endless belt-shaped secondary transfer belt 24 between two rollers 23, and one of the rollers 23 is placed on the third support roller 16 via the intermediate transfer member 10. It is arranged by pressing. The image on the intermediate transfer body 10 is transferred by the secondary transfer device 22 to a sheet S (see FIG. 2) as a recording medium fed from the feed table 2.
On the left side of the secondary transfer device 22, a fixing device 25 for fixing a transfer image on a sheet is provided. The fixing device 25 has a configuration in which a pressing roller 27 is pressed against a fixing belt 26 having an endless belt shape.
[0062]
The secondary transfer device 22 also has a sheet conveyance function of conveying the sheet S after image transfer to the fixing device 25. Of course, a transfer roller or a non-contact transfer charger may be disposed as the secondary transfer device 22. However, if the belt transfer structure is used as described above, the advantage that the sheet transfer function to the fixing device 25 can be obtained at the same time. There is.
In the present embodiment, under the secondary transfer device 22 and the fixing device 25, a sheet reversing device 28 that reverses the sheet S when recording images on both sides of the sheet S substantially in parallel with the tandem image forming device 20 described above. Is provided.
[0063]
When making a copy using the above-described color copying machine, an original is set on the original table 30 of the automatic original transport device 4. Alternatively, the automatic document feeder 4 is opened, a document is set on the contact glass 32 of the scanner 3, and the automatic document feeder 4 is closed to hold the document. When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 4, the document is automatically conveyed and moved onto the contact glass 32, and then set on the other contact glass 32. Then, the scanner 3 is immediately driven, and the first traveling body 33 and the second traveling body 34 start traveling.
The first traveling body 33 irradiates light from the light source and further reflects the light reflected from the document surface to the second traveling body 34, reflects it on the mirror of the second traveling body 34, and reads it through the imaging lens 35. The document is read by the sensor 36 and read.
[0064]
When a start switch (not shown) is pressed, one of the support rollers 14, 15, 16 is driven to rotate by a drive motor as drive means (not shown), and the other two support rollers are driven to rotate, and the intermediate transfer is performed. The body 10 is driven to rotate. At the same time, in each of the image forming units 18Y, 18C, 18M, and 18Bk, the corresponding photoconductors 40Y, 40C, 40M, and 40Bk rotate, and yellow, cyan, and yellow are respectively formed on the photoconductors 40Y, 40C, 40M, and 40Bk. A monochromatic image of magenta and black is formed. Image formation is performed by a known process.
That is, first, the surfaces of the photoconductors 40Y, 40C, 40M, and 40Bk are uniformly charged by the charging rollers 60Y, 60C, 60M, and 60Bk. Irradiation of writing light LY, LC, LM, LBk by the above-mentioned method forms an electrostatic latent image on the photoconductors 40Y, 40C, 40M, 40Bk. Thereafter, toner is adhered by the developing devices 61Y, 61C, 61M, and 61Bk, and the electrostatic latent images are visualized to form yellow, cyan, magenta, and black on the photoconductors 40Y, 40C, 40M, and 40Bk, respectively. Is formed.
As the intermediate transfer body 10 is transported, the single-color images are sequentially transferred by the primary transfer rollers 62Y, 62C, 62M, and 62Bk as primary transfer means to form a composite color image on the intermediate transfer body 10.
The toner remaining on the surfaces of the photoconductors 40Y, 40C, 40M, and 40Bk after the image is transferred is cleaned by the photoconductor cleaning devices 63Y, 63C, 63M, and 63Bk. After that, the surface potentials of the photoconductors 40Y, 40C, 40M, and 40Bk are initialized by the charge removing devices 64Y, 64C, 64M, and 64Bk to prepare for another image formation.
On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 2 is selectively rotated, and the sheet S is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages. Then, the sheets are separated one by one by a separation roller 45 and conveyed to a sheet feeding path 46. The sheet S is conveyed by conveying rollers 47, guided to a paper feed path 48 in the copying machine main body 1, and temporarily stopped by a pair of registration rollers 49. Here, the leading end of the sheet S is abutted against the nip portion of the registration roller pair 49 by a predetermined excessive feed, and the skew is corrected. Alternatively, the sheet feed roller 50 is rotated to feed out the sheets S on the manual feed tray 51, separated by the separation roller 52 one by one, and conveyed to the manual feed path 53. The conveyed sheet S is once stopped by the registration roller pair 49.
[0065]
The registration roller pair 49 is driven to rotate in synchronization with the composite color image on the intermediate transfer member 10, and the sheet S is fed between the intermediate transfer member 10 and the secondary transfer device 22. The color image is transferred onto S.
The sheet S after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25, where the transferred image is fixed by applying heat and pressure by the fixing device 25, and then conveyed by the switching claw 55. The direction is switched and the sheet is discharged by the discharge roller pair 56 and is stacked on the sheet discharge tray 57. Alternatively, the conveyance path is switched by the switching claw 55 and the sheet is fed into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and the image is also recorded on the back surface. 57.
The intermediate transfer body 10 after the image transfer has the residual toner remaining on the intermediate transfer body 10 removed by the intermediate transfer body cleaning device 17 after the image transfer, and is ready for the image formation by the tandem image forming apparatus 20 again.
[0066]
Based on FIG. 2, the configurations of the developing devices 61Y, 61C, 60M, and 60Bk and the photoconductor cleaning devices 63Y, 63C, 63M, and 63Bk will be described in further detail. Note that the configuration corresponding to the yellow image will be described as a representative, and the other configuration is the same.
The developing device 61Y includes a developing sleeve 61Y-1 for supplying toner to the photoconductor 40Y, a first stirring and conveying member 61Y-2, and a second stirring and conveying member 61Y-3. The first stirring / transporting member 61Y-2 and the second stirring / transporting member 61Y-3 transfer and circulate the developer between the front side and the back side in the longitudinal direction (the photoreceptor rotation axis direction). In addition, on the second stirring and conveying member 61Y-3 side, new toner or collected toner described later is supplied and mixed with the circulating developer flow.
[0067]
The photoreceptor cleaning device 63Y includes a cleaning blade 63Y-1 provided with its tip pressed against the photoreceptor 40Y, and a conductive fur brush provided so that the outer periphery thereof is in contact with the photoreceptor 40Y in order to enhance cleaning performance. (Cleaning brush) 63Y-2, toner recovery coil 63Y-3 and the like. The cleaning blade 63Y-1 can be formed of, for example, polyurethane rubber. The fur brush 63Y-2 is provided so as to rotate in the counter direction with respect to the photoconductor 40Y.
The residual toner on the photoreceptor 40Y removed by the cleaning blade 63Y-1 and the fur brush 63Y-2 is conveyed by the toner collecting coil 63Y-3 and, as shown in the Bk image forming means, becomes the second toner supply unit also serving as the developer supply unit. The toner is returned to the developing device 61Y by the toner recycling means 80 connecting the second stirring and conveying member 61Y-3 side, and is used again for development. Although omitted in the figure, the toner recycling unit 80 is provided individually for each of the image forming units 18Y, 18C, 18M, and 18Bk.
[0068]
Further, in the present embodiment, as shown in FIG. 2, a latent image carrier discharging means for suppressing reverse transfer is provided at a position after the development process of the second and subsequent photoconductors 40C, 40M, and 40Bk and before the transfer process. 101C, 101M and 101Bk are provided. Since the problem of reverse transfer does not occur in the transfer of the first color, the image forming means corresponding to the yellow image of the first color is not provided with the latent image carrier discharging means.
At a position facing the support roller 15, a corotron 102 is provided as an intermediate transfer member discharging means (omitted in FIG. 1).
[0069]
Before transferring the cyan toner image from the photoconductor 40C to the intermediate transfer body 10, the surface potential of the photoconductor 40C is removed by the latent image carrier discharging means 101C, and the magenta toner image is transferred from the photoconductor 40M to the intermediate transfer body 10. Before the transfer, the surface potential of the photoconductor 40M is eliminated by the latent image carrier discharging means 101M, and before the black toner image is transferred from the photoconductor 40Bk to the intermediate transfer member 10, the photosensitive member is discharged by the latent image carrier discharging means 101Bk. The surface potential of 40 Bk is eliminated.
[0070]
As the latent image carrier static elimination means (light irradiation device) 101, an LED, an LD, a xenon lamp, or the like can be used. It is possible to control the surface potential of the photoreceptor to an arbitrary value by grasping in advance the relationship between the current or applied voltage flowing to the LED or LD and the amount of light emission (exposure), and adjusting the amount of light emission to control the amount of charge removed. It is.
[0071]
FIG. 3 is a graph of an experimental result showing a relationship between a surface potential difference between an image portion and a non-image portion of the photoconductor and a reverse transfer amount. Normally, after the developing step and before the transfer step, the surface of the photoreceptor is neutralized to lower the absolute value of the potential. As shown in FIG. 3, reverse transfer is more likely to occur when the absolute value of the surface potential of the photoreceptor is suppressed. Can be suppressed.
In the experiment shown in FIG. 3, the static electricity was removed by using a red LED. The surface potential on the photoreceptor of the image portion was -150 [V]. As described above, since the toner is not reversely transferred to the image portion having a low potential, the surface potential difference of the photosensitive member is desirably suppressed to 200 [V] or less, thereby preventing the reverse transfer and preventing the image from being disturbed. Can obtain a perfect image.
[0072]
Basically, as shown in FIG. 3, the lower the surface potential of the photoreceptor, the less reverse transfer occurs. However, if the amount of light is increased too much and the photoreceptor is irradiated, the photoreceptor may be damaged and the service life may be significantly shortened. Therefore, it is necessary to set an appropriate range.
As is well known, some materials used as photoreceptors exhibit a photo-fatigue phenomenon in which irradiation with light increases the capacitance of the photoconductive layer and decreases the electrical resistance. The photoreceptor portion below the image does not receive much light due to the filter effect of the visible image, but the non-image portion is irradiated with light several times stronger than the exposure light. Therefore, light irradiation other than writing exposure may be desired to be avoided as much as possible.
It is desirable that the charge removal step on the photoreceptor be performed after the development step and before the transfer step. If the non-image portion potential is low, reverse transfer is unlikely to occur, but in the developing step, the larger the potential contrast between the image portion and the non-image portion, the better development can be made without soiling or the like. Therefore, by performing the charge removal after the development step, it is possible to achieve both good development and prevention of reverse transfer.
[0073]
In the present embodiment, the relationship between the current or applied voltage flowing through the latent image carrier static elimination means 101 and the amount of light emission (exposure) is grasped in advance by experiments or the like (including computer simulation), and the amount of light emission and the amount of charge to be eliminated are determined. Is stored in, for example, a ROM of a control means (not shown) so as to perform optimal static elimination for each color.
[0074]
The amount of charge removal by the latent image carrier discharging means 101 is also related to the amount of charge of the intermediate transfer member 10. Since the amount of charge of the intermediate transfer member 10 changes as the number of transfers increases, the above relational data table takes this point into consideration. It is desirable to obtain experimental data.
[0075]
Here, the control means is a microcomputer including a CPU, a RAM, a ROM, an I / O interface, and the like, and can be also used as a main controller of the color copying machine.
[0076]
In the present embodiment, as the intermediate transfer body 10, the area resistivity of the back surface is 10 ⁹ [Ω / □] or more, volume resistivity is 10 ^Thirteen A belt of [Ωcm] or more is employed. Here, the unit of the sheet resistivity is a dimensionless system, but the unit is described as [Ω / □] for convenience to distinguish it from the normal resistivity.
[0077]
As shown in FIG. 3, reverse transfer can be suppressed when the absolute value of the photoconductor surface potential is suppressed low. However, if the non-image portion potential is excessively removed, toner dust due to the pre-transferred toner adhering to the non-image portion region on the intermediate transfer member increases.
[0078]
As shown in FIG. 4, it has been confirmed by experiments by the present inventors that the occurrence of such image quality deterioration becomes more remarkable as the charge of the photoconductor is removed. Therefore, it is desirable that the potential of the image portion and the potential of the non-image portion are substantially equal, or that the potential of the non-image portion is larger when comparing the absolute values.
[0079]
As described above, although the charge removal before the transfer process is effective in preventing the reverse transfer, the toner dust due to the pre-transfer increases. In order to suppress the toner dust, the pre-transfer itself that causes the toner dust may be prevented.
[0080]
The pre-transfer occurs mainly due to an unnecessary electric field formed by a wraparound of a bias applied to the intermediate transfer member before the transfer step. In order to prevent this pre-transfer from occurring, in the present embodiment, as described above, the intermediate transfer body 10 has a rear surface resistivity of 10%. ⁹ [Ω / □] or more, volume resistivity is 10 ^Thirteen A belt having a resistance of [Ωcm] or more (hereinafter referred to as “high resistance belt”) was employed.
[0081]
The reason for setting the resistance value of the intermediate transfer member 10 as the resistance value of the back surface of the intermediate transfer member 10 as described above is that a bias is normally applied from the back surface of the belt when the toner is transferred from the photoconductor 40 to the intermediate transfer member 10. is there. In particular, when the belt is composed of a plurality of layers made of different materials, it is necessary to consider the resistance of the layer (base layer) closest to the bias applying member, in which current flows first when a bias is applied. is there.
[0082]
FIG. 5 shows the relationship between the above-described medium-resistance belt / indirect transfer method and the occurrence of dot dust in the high-resistance belt / direct transfer method in a case where the charge is removed before the transfer by the latent image carrier discharging means and a case where the charge is not removed. 6 is a graph showing the results of an experiment.
[0083]
As is clear from FIG. 5, in the case of the high-resistance belt, a medium-resistance belt having a lower resistance (having a sheet resistivity of 10 ⁸ [Ω / □] or less, volume resistivity of 10 ¹² [Ωcm] or less, the amount of dust is small.
This is because the high resistance belt has a high resistance, so that the charge wraparound is small and the transfer electric field does not leak, so that the pre-transfer in which the toner jumps before the transfer step does not occur. Since the pre-transfer phenomenon itself, which is one of the causes of dust, does not occur, a good image can be obtained.
Further, a red LED (latent image carrier removing means) was installed at a position after the developing step and before the transfer step, and the amount of dust when the photosensitive member was subjected to light removal was compared. In this case, since pre-transfer hardly occurs, there is little cause of toner dust, and dust is hardly generated. The effect is obvious compared to the medium resistance belt.
[0084]
As described above, when a color image is created, the image to be transferred from the photoreceptor to the intermediate transfer member is maintained under the condition that dust does not occur, and reverse transfer is not caused. May not use a certain color. In such a case, since no toner image is formed on the photoconductor, dust does not need to be considered.
[0085]
Therefore, it is possible to set all or individual process conditions differently from the normal conditions, and set the conditions so as to minimize the reverse transfer.
For example, the closer the non-image portion potential of the photoconductor is to 0 [V], the better. When there is an image, the potential can be reduced only to about -150 to -250 [V] of the image portion potential. However, when there is no image, the reverse transfer is further prevented by discharging the photosensitive member more strongly. Easier to do.
Also, if a transfer bias is applied more than necessary, reverse transfer is likely to occur, so that it is also effective to change to a lower set value.
[0086]
From such a viewpoint, it is determined whether or not there is an unused color based on the information read by the scanner 3 on the document, and if there is an unused color, the latent image carrier discharging means 101 corresponding to that color is most often used. What is necessary is just to set and control the conditions so as not to perform reverse transfer.
[0087]
When a color image is created, there is no problem of reverse transfer in the first transfer of the first color. Therefore, in order to reduce the cost, it is desirable to install the latent image carrier static elimination means in the photoconductor units (image forming means) for the second and subsequent colors. However, in order to use the four photoconductor units in common, an LED may be installed in the first color unit. In this case, the LED corresponding to the first color unit is controlled by the control means. Should not be turned on.
[0088]
In the present embodiment, in order to further suppress the occurrence of reverse transfer, a toner having a high circularity (average circularity of 0.94 or more) is used. The reason will be described below.
[0089]
The degree of circularity of the toner is determined, for example, by arbitrarily selecting the shape of a large number of toner particles observed with a scanning electron microscope or an optical microscope, using a commercially available image analyzer or flow-type particle image analyzer, for example, manufactured by SysMex. May be evaluated by FPIA-1000 or the like, and is given by the following formula. This is an apparatus that images thousands of particles in a liquid and performs image analysis and particle size analysis.
[0090]
Circularity = Σ [(4 · π · Si) / Li2] / N
Here, Li represents the perimeter of each particle in the projected image, Si represents the projected area of each particle, and N represents the total number of evaluated particles. As the degree of circularity approaches 1, the toner approaches a true sphere.
[0091]
The reason that the spherical toner having an average circularity of 0.94 or more has less reverse transfer is that the adhesive force between the toner and the photoconductor greatly contributes to the reverse transfer. This is because the van der Waals force becomes smaller.
As shown in FIG. 6A, the toner T1 having an average circularity of 0.94 or less has a contact area with the photoreceptor 40 of A1, whereas the average circularity is as shown in FIG. 6B. With the toner T2 of 0.94 or more, the contact area with the photoconductor 40 becomes as small as A2.
The van der Waals force generally decreases as the contact area with the opposing object (in this case, the photoconductor) decreases. The more spherical the toner, the smaller the contact area of the toner itself.
[0092]
Generally, additives such as silica and titanium oxide are added to the toner in order to increase the fluidity of the toner and reduce the adhesive force (cohesion) between the toners. However, as shown in FIG. Is 0.94 or more, the probability that the portion of the additive (the portion indicated by the symbol ad in FIG. 7) on the surface of the toner T2 becomes a portion that comes into contact with the photoconductor 40 increases. Is sufficiently smaller than the toner particle size, so that the apparent van der Waals force is reduced.
[0093]
It has been confirmed by the present inventors that the closer the toner is to a spherical toner having an average circularity of 0.94 or more, the more the occurrence of reverse transfer can be prevented.
[0094]
It is considered that the toner having a nearly spherical shape has a smaller adhesive force because the effect of the external additive added to the toner is stronger as described above. If the adhesion to the photoreceptor is small, it is expected that the transfer rate will be good and that reverse transfer will not easily occur.
Table 1 shows the results of measuring the reverse transfer rate under normal conditions by producing a prototype toner having an actually changed shape.
[0095]
[Table 1]

[0096]
From the results shown in Table 1, when the average circularity is 0.94 or more, the reverse transfer is remarkably better than that when the average circularity is less than 0.94. .94 or more.
[0097]
The static elimination used for the reverse transfer prevention is also performed for the intermediate transfer body, and the configuration will be described below.
Normally, in a tandem type image forming apparatus, since there are a plurality of transfer steps, the belt portion which has been transferred and moved downstream from the transfer position is charged with the charge received at the time of transfer, and the next toner image is not changed. When the transfer is performed, the transfer performance may be impaired due to the influence of the previous transfer charging.
Particularly, in the case of a high resistance belt, self-discharge is difficult, and thus the need for a charge removing means is high. From this point of view, in the present embodiment, as shown in FIG. 2, a corotron 102 is provided as an intermediate transfer body charge removing unit.
[0098]
Using a supporting roller 15 as a driving roller facing the corotron 102, AC was superimposed on DC, and static electricity was removed with an AC bias of 5.8 [kV] and a DC bias of 600 [V], and good results were obtained. . When the “peak-to-peak” voltage of the AC bias exceeds a certain value, the charging potential is saturated, and the saturation potential substantially matches the DC component.
Even if the driving roller 15 is not used as the opposing member, the corotron 102 can be installed at another place by installing another opposing member. The corotron 102 is desirably located at the most upstream part of the transfer part (in the configuration shown in FIG. 1, upstream of the image forming unit corresponding to the yellow image) after the intermediate transfer body cleaning device 17. The corotron 102 may be provided on the back side of the intermediate transfer body 10.
[0099]
Regarding the latent image carrier discharging means 101 and the intermediate transfer body discharging means (member indicated by reference numeral 102 in FIG. 2), the following configuration can be adopted.
In the embodiment shown in FIGS. 1 and 2, a light irradiating device such as an LED, an LD, or a xenon lamp is used as the latent image carrier discharging means. There is also a method. For example, by using a corotron or the like, positive and negative ions can be generated by applying an AC bias or the like, and the positive ions can be supplied to the non-image area to eliminate static electricity. In this configuration, since the potential of the non-image area is higher than that of the image area to which the toner is attached, the generated ions are selectively adsorbed to the non-image area and are discharged.
It is also possible to use a scorotron or the like to set the grid potential to the same polarity as the potential of the image to which the toner adheres, and to set the absolute value slightly higher to generate ions opposite in polarity to the toner to eliminate electricity. It is.
[0100]
In the embodiment shown in FIGS. 1 and 2, the corotron 102 is used as the intermediate transfer member static elimination means, but a fixed brush in which conductive fibers are bundled in a brush shape may be used.
[0101]
Alternatively, as shown in FIG. 8, for example, a rotating brush 82 in which conductive fibers are implanted in a cloth and rolled around conductive rollers may be used.
In each case, a DC voltage of about 0.5 to 2 [kV] is applied to the brush by a power source (not shown), and the leading end of the brush contacts the intermediate transfer belt 10.
At the leading end, electrons and ions move due to the generation of electric charges due to friction with the intermediate transfer belt 10, the injection of electric charges, or the discharge in a minute area, and the intermediate transfer belt 10 is discharged.
[0102]
As shown in FIG. 9, a configuration may be adopted in which a voltage is applied to the conductive blade 83 by a power supply (not shown).
[0103]
The intermediate transfer member may be configured to apply a voltage to a conductive roller as a neutralization unit. When a roller is used, a voltage is applied to a conductive rubber roller, and the roller is pressed against the intermediate transfer belt 10 to remove electricity. Basically, charge transfer is caused by discharge in a minute gap, and either a DC bias application method or an AC superposition method is possible. Desirably, an AC superposition method in which uniform charging is relatively easy is preferable.
[0104]
The contact-type intermediate transfer member static elimination method has been described above. However, the intermediate transfer member static elimination means may be held in a non-contact state with the intermediate transfer member 10. In this case, since the intermediate transfer member static elimination means is not contaminated by foreign matters such as toner on the intermediate transfer member 10, the deterioration of the charging performance over time due to dirt can be suppressed, and high quality of the intermediate transfer member static elimination function can be obtained. At the same time, it is possible to improve the durability of the intermediate transfer body discharging means.
[0105]
For example, as shown in FIG. 10, a resin tape 85 with an adhesive layer having a uniform thickness, for example, as a spacing member, is provided on an outer peripheral surface of an end portion (a portion corresponding to a non-image area of the intermediate transfer body 10) of the conductive roller 84. Is applied in the circumferential direction so as to maintain a gap g between the intermediate transfer body 10. In this case, since the static elimination potential is reduced by the amount of the gap g, the thickness of the resin tape 85 is preferably up to about 85 [μm].
In the case where a roller is used as the intermediate transfer body discharging means, it is desirable to drive the intermediate transfer body 10 at the same speed as that of the intermediate transfer body 10 so as to minimize friction with the intermediate transfer body 10. That is, as shown in FIG. 11, a configuration in which the sawtooth discharge needle 86 is provided in a non-contact state with the intermediate transfer body 10 and a voltage is applied by a power supply (not shown) may be adopted.
[0106]
The intermediate transfer member static elimination means such as the rotating brush 82, the blade 83, the conductive roller 84, and the discharge needle 86 may be provided on the back side of the intermediate transfer member 10. In this case, the space inside the intermediate transfer body 10 can be used, so that the configuration can be made compact. When a roller such as the conductive roller 84 is used as the intermediate transfer member static elimination means, the roller may be provided so as to also serve as a support roller for the intermediate transfer member 10.
[0107]
In the present embodiment, as a method for suppressing the generation of toner dust, in addition to the above-described resistance characteristics of the intermediate transfer member, the toner on the latent image carrier does not transfer to the intermediate transfer member before the primary transfer process is performed. In this state, the surface potential of the intermediate transfer member is controlled.Specifically, a bias for attracting toner from the intermediate transfer member to the latent image carrier, that is, a counter bias for forming an electric field opposite to the transfer bias is applied. Thus, the surface potential is controlled. Hereinafter, the counter bias will be described.
12 to 17 are schematic diagrams for explaining a method for suppressing transfer dust due to pre-transfer generated at the entrance of the transfer nip.
When the toner charge polarity is negative, in a system using reversal development, the charge potential of the photoreceptor is also negative, and the image portion recorded as a latent image by light exposure does not completely lose the potential by exposure but remains as a residual potential. A potential of about -50 to -70 [V] remains. Since the toner of the negative polarity is developed in this portion, the image area becomes about -150 to -250 [V] after the development (however, it depends on the charge amount and weight of the toner to be developed).
On the other hand, the surface potential of the intermediate transfer body near the entrance of the transfer nip depends on the system, but a positive bias for transfer is leaking. Is worse, the voltage may be about +500 [V].
[0108]
Due to the relationship between the image portion potential on the photoconductor and the surface potential of the intermediate transfer body, the electric field generated is on the side where the toner moves from the photoconductor to the intermediate transfer body, as shown in FIG. Flies before transcription and becomes chile.
Therefore, as shown in FIG. 13, the surface potential of the intermediate transfer member before the transfer nip is set lower than the potential of the image portion on the photoconductor so that an electric field in which the toner transfers from the photoconductor to the intermediate transfer member is not generated. By controlling the surface potential, the direction of the electric field is opposite to that in the case shown in FIG. 12, as shown in FIG. 12, and acts in the direction of pressing (pulling) the toner to the photoreceptor to generate dust. do not do. In FIG. 13, a conductive blade to which a surface potential is controlled, that is, a voltage is applied as a configuration for applying a counter bias (for convenience, the name is denoted by reference numeral 150 in FIG. 13 and is referred to as a counter bias blade) ) Is shown.
[0109]
In order to control the surface potential of the intermediate transfer belt by using the principle of the counter bias transfer method, a method of directly applying a voltage to the surface of the intermediate transfer body by some means and a method of controlling the surface potential before entering the transfer nip are described. The method is roughly divided into a method of controlling the surface of the intermediate transfer member by charging it to a predetermined potential.
In the former method, for example, as shown in FIG. 14, an intermediate transfer belt is used as an intermediate transfer member, and a roller which is a conductive member (for convenience, has the same function as the blade shown in FIG. 13) near the back of the transfer nip entrance. There is a method in which a voltage is applied to the surface of the intermediate transfer belt by applying a bias to the roller so as to be able to follow the member, which is denoted by reference numeral 150 ′). The simplest method is that the roller can be moved (followed) at the same speed as the intermediate transfer member, and there is no fear of damaging the back surface of the intermediate transfer belt. Cannot slim, so it takes up some space.
In order to perform the transfer, it is necessary to provide a conductive member for applying a transfer bias near the transfer nip outlet, but there is also a drawback that the member must not interfere with this member.
Therefore, a plate-shaped conductive member, for example, a SUS plate having a thickness of about 0.1 [mm] to about 0.5 [mm] (the tip is preferably rounded with a file or the like to prevent damage) or An equivalent effect can be obtained by fixing and installing a conductive rubber or conductive resin plate and applying a bias to the member. In this case, unlike the roller, the plate-like member can be set up to the very end of the transfer nip, so that the effect is large, the cost is low, and the space is created.
[0110]
Materials for conductive rubber and resin other than metal include polyurethane, polyurea, silicon, NBR, CR, fluororubber, fluororesin, polycarbonate, nylon, polypropylene, polyethylene, and other conductive materials such as carbon and fine metal powder. In some cases, conductive fillers are dispersed to impart conductive properties. There is also an epichlorohydrin rubber which has ionic conductivity itself. Since these plate-shaped members are fixed and are always in contact with the back surface of the intermediate transfer belt, those having mechanical strength and a low coefficient of friction are desirable. For this reason, a fluorine-based material or the like is desirable. Otherwise, a treatment for reducing friction may be performed on the contact portion.
Even if such a process is performed, since the fixing member always comes into contact with the back surface of the intermediate transfer belt, there is a possibility that the back surface of the belt may be damaged when foreign matter or the like is caught or with time. Such a problem can be solved by using a conductive brush, and also saves space.
[0111]
However, in this case as well, there is a characteristic in any of the methods, such as a possibility that the hair of the brush may come off, so that it is preferable to select the method according to the case.
[0112]
As a method of charging the surface of the intermediate transfer member, which is used as another method of controlling the surface potential of the intermediate transfer member, a method of charging with a corona charger or the like as shown in FIG. 15 is typical. In this case, it is desirable to adjust the potential to a predetermined value using a scorotron-type charger (for convenience, indicated by reference numeral 150A in FIG. 15).
In recent years, some charger-based chargers have been shunned because of the generation of ozone, but as an alternative device, as shown in FIG. 16, a contact roller charging member (for convenience, indicated by reference numeral 150B in FIG. 16). ). In this case, the bias applied to the roller is also negative because the surface of the intermediate transfer belt is desired to be negatively charged. The toner also has a negative polarity, so there is no risk of toner being attracted to the roller member.However, even if there is no fear of electrostatic attraction, an image is inevitably formed when a linear velocity difference occurs between the roller and the surface of the intermediate transfer belt. It will be disturbed.
Therefore, as shown in FIG. 17, a non-contact charging method in which a voltage is applied to a conductive member (indicated by reference numeral 150C in FIG. 17 for convenience) and charged from the intermediate transfer belt so as to be in non-contact, is also conceivable. .
For example, a conductive NBR coating (volume resistance of 10 ⁷ [Ωcm]) A gap tape for maintaining a non-contact state is wound around the end of the roller with a thickness of 50 [μm], and this tape portion is pressed against a non-charging member to apply a bias. , And the toner can be charged without contact between the toner on the intermediate transfer belt and the charging member during color image formation. The method shown in FIGS. 15 to 17 can be selected in consideration of use conditions and the like.
[0113]
With the configuration and method described above, it is possible to suppress the occurrence of reverse transfer with high accuracy while keeping the image in good condition, that is, while suppressing the occurrence of toner dust with high accuracy.
Therefore, the problem of color mixing of waste toner due to reverse transfer can be solved. Therefore, in a so-called tandem-type intermediate transfer image forming apparatus provided with a developing device for one color per photoconductor, the waste toner collected by the photoconductor cleaning device 63 is a toner of the color developed by the photoconductor. Thus, even if the toner is returned to the developing device 61 and reused, there is no problem in image quality such as a change in color, and the toner can be recycled. As a result, the amount of waste toner discharged can be significantly reduced, the environmental load can be reduced, and there are merits such as a reduction in cost and labor for the user.
However, even if there is no reverse transfer toner, in a so-called one-drum type image forming apparatus (described later) in which one photosensitive member is provided with a plurality of developing devices, since there is only one photosensitive member, the photosensitive member is used for forming an image of each color. The transfer residual toner remaining on the body is collected by one cleaning device, and the respective colors are mixed, so that it is difficult to reuse the toner. That is, the effective use of the toner recycling unit 80 described above is substantially limited to the tandem type.
[0114]
Next, an example of application to a so-called one-drum type color image forming apparatus having one photoconductor and a plurality of developing devices will be described with reference to FIG.
In a color copying machine as an image forming apparatus according to the present embodiment, a writing optical unit 400 as an exposure unit converts color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to a document image, and performs latent writing. An electrostatic latent image is formed on a photosensitive drum 402 as an image carrier.
[0115]
The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 thereof, an f / θ lens 410, a reflection mirror 412, and the like.
The photoconductor drum 402 is rotated in a counterclockwise direction as indicated by an arrow, and a photoconductor cleaning unit 414, a static elimination lamp 416, a potential sensor 420, and a rotary developing device 422 are selected around the photoconductor drum 402. A developing device (a developing device 438 in FIG. 15), a development density pattern detector 424, a latent image carrier discharging unit 425, an intermediate transfer belt 426 as an intermediate transfer member, and the like are arranged. The intermediate transfer belt 426 is a high resistance belt similar to the intermediate transfer body 10 in the first embodiment.
[0116]
The rotary developing device 422 includes a black developing device 428, a cyan developing device 430, a magenta developing device 432, a yellow developing device 434, and a rotation drive unit (not shown) for rotating each developing device.
In the standby state, the rotary developing device 422 is set at the position of black development, and when a copying operation is started, reading of black image data is started at a predetermined timing by the color scanner 200, and this image data is read. , The formation of the optical writing / electrostatic latent image (black latent image) by the laser beam starts.
[0117]
In order to develop from the leading end of the black latent image, before the leading end of the latent image reaches the developing position of the black developing device 428, the rotation of the developing sleeve is started to develop the black latent image with black toner. An image of negative polarity toner is formed on the photosensitive drum 402.
Thereafter, the developing operation of the black latent image area is continued, but when the rear end of the latent image passes the black developing position, the rotary developing operation is promptly performed from the developing position for black to the developing position for the next color. The device 422 rotates. This operation is completed at least before the leading end of the latent image based on the next image data arrives.
[0118]
When the image forming cycle is started, first, the photosensitive drum 402 is rotated in a counterclockwise direction as indicated by an arrow, and the intermediate transfer belt 426 is rotated in a clockwise direction by a drive motor (not shown). With the rotation of the intermediate transfer belt 426, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), and magenta (M) , Yellow (Y) in this order on the intermediate transfer belt 426 (primary transfer) to form a toner image.
As in the embodiment shown in FIGS. 1 and 2, after the developing process of each toner image and before the transferring process to the intermediate transfer member 426, the surface of the photosensitive drum 402 is removed by the latent image carrier discharging unit 425. The potential is eliminated.
[0119]
The intermediate transfer belt 426 includes a primary transfer bias roller 450 as a primary transfer unit facing the photosensitive drum 402, a driving roller 444, a secondary transfer facing roller 446 facing the secondary transfer roller 454, and an intermediate transfer belt 426. It is stretched between the respective support members of the cleaning opposed roller 448A facing the cleaning means 452 for cleaning the surface, and is driven and controlled by a drive motor (not shown).
The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image. This belt transfer image is collectively transferred to a sheet as a recording medium by a secondary transfer opposing roller 446.
[0120]
Each of the recording paper cassettes 458, 460, and 462 in the paper supply bank 456 stores various sizes of paper different from the size of the paper stored in the cassette 464 in the apparatus main body. The designated sheet is fed and conveyed from the size paper storage cassette toward the registration roller pair 470 by the sheet feeding roller 466. In FIG. 18, reference numeral 468 denotes a manual paper feed tray for OHP paper, thick paper, and the like.
At the time when the image formation is started, the paper is fed from the paper feed port of any one of the cassettes, and waits at the nip portion of the pair of registration rollers 470. When the leading end of the toner image on the intermediate transfer belt 426 approaches the secondary transfer opposing roller 446, the registration roller pair 470 is driven so that the leading end of the sheet coincides with the leading end of the image, and the registration of the sheet and the image is adjusted. Is performed.
[0121]
In this way, the sheet is superimposed on the intermediate transfer belt 426 and passes under the secondary transfer opposing roller 446 to which a voltage having the same polarity as that of the toner is applied. At this time, the toner image is transferred to the paper. Subsequently, the paper is discharged, separated from the intermediate transfer belt 426 and moved to the paper transport belt 472.
The sheet on which the four-color superimposed toner image has been collectively transferred from the intermediate transfer belt 426 is conveyed by a paper conveying belt 472 to a fixing device 470 of a belt fixing system, and the fixing device 470 fixes the toner image by heat and pressure. The sheet on which fixing has been completed is discharged out of the apparatus by a discharge roller pair 480 and stacked on a tray (not shown). Thereby, a full-color copy is obtained.
[0122]
Due to the characteristics of the high resistance belt, it is desirable that the transfer bias by the primary transfer bias roller 450 be applied directly to the back surface at the position where the photosensitive drum 402 and the intermediate transfer belt 426 are in contact with each other. A modified example of the latent image carrier static elimination means, and the static elimination configuration of the intermediate transfer belt 426 can be implemented in the same manner as described above. FIG. 18 shows a counter bias configuration using rollers by reference numeral 150 'used in FIG. In this configuration, for the intermediate transfer belt 426, generation of toner dust is prevented by the principle and mechanism shown in FIGS.
[0123]
【The invention's effect】
According to the first and twentieth aspects of the present invention, before the primary transfer of the toner image to the intermediate transfer member, the charge elimination process of the latent image carrier is performed, and the toner carried on the latent image carrier is removed from the intermediate transfer member. The surface potential of the intermediate transfer member is controlled so as not to transfer to the toner. In the invention according to the twentieth aspect, control is performed such that the toner has the same polarity as the toner on the latent image carrier side and the absolute value is equal to or higher than the charging potential of the toner. The direction of the electric field formed between the latent image carrier and the intermediate transfer member can be set to a direction in which the toner does not fly to the intermediate transfer member. As a result, the flying of the dusty toner to the intermediate transfer body side is suppressed, and both the prevention of reverse rotation of the latent image carrier due to the charge removal process and the prevention of toner dust due to the pre-transfer can be achieved, and the image quality can be improved. Can be prevented from deteriorating.
[0124]
According to the second and third aspects of the present invention, pre-transfer can be efficiently prevented by setting the sheet resistivity and / or volume resistivity on the back surface of the intermediate transfer member to a predetermined value.
[0125]
According to the fourth aspect of the invention, by defining the potential difference between the image portion and the non-image portion on the latent image carrier side, it is possible to increase the efficiency of preventing reverse transfer.
[0126]
According to the fifth aspect of the present invention, since the charge elimination process of the latent image carrier can be performed by a simple configuration of light irradiation, the charge elimination can be reliably performed even when the installation location of the configuration for performing the charge elimination process is narrow. And the potential difference between the image portion and the non-image portion can be set to a default value.
[0127]
According to the sixth aspect of the present invention, by performing the charge elimination process using ions, it is possible to reduce the photo fatigue of the photosensitive layer, which is likely to occur when the latent image carrier is irradiated with light more than necessary. As a result, the life of the latent image carrier can be extended.
[0128]
According to the seventh aspect of the invention, by defining the execution time of the charge removal step, the potential difference between the image portion and the non-image portion on the latent image carrier side is defined during the transfer process performed after the development process. This means that the primary transfer process can be executed in a state where the reverse vehicle generated due to a large potential difference is reliably suppressed.
[0129]
According to the eighth aspect of the invention, the amount of power failure used in the charge removal process is defined to be an amount corresponding to the information of the image, so that light fatigue undesired on the latent image carrier side can be reduced and reverse transfer can be prevented. Energy loss can be suppressed.
[0130]
According to the ninth aspect of the present invention, since the charge elimination process is performed at the time of image transfer of the second and subsequent colors except for the first color in which charge accumulation does not occur, energy consumption for preventing reverse transfer is minimized. , Energy loss can be reduced.
[0131]
According to the tenth aspect of the present invention, since the charge removal process can be performed also for the intermediate transfer member, it is possible to obtain a good transfer image by eliminating the adverse effect on the next transfer process due to the charge remaining on the intermediate transfer member. Becomes possible.
[0132]
According to the eleventh aspect, by using the corotron method for neutralization of the intermediate transfer body, it is possible to easily apply a predetermined potential.
[0133]
According to the twelfth aspect of the present invention, the static elimination in the intermediate transfer member is performed by using a configuration for applying a voltage to the conductive brush. Can be applied, thereby simplifying the configuration and extending the life of the intermediate transfer member.
[0134]
According to the thirteenth aspect of the present invention, since the charge elimination in the intermediate transfer member is performed by using a configuration for applying a voltage to the conductive blade, the charge can be easily disposed on the back surface of the intermediate transfer member. The simplification and the freedom in layout of the intermediate transfer member static elimination configuration can be improved.
[0135]
According to the fourteenth aspect of the present invention, since the charge elimination in the intermediate transfer member is performed by using a configuration in which a voltage is applied to the conductive roller, the intermediate transfer member is driven at a constant speed to thereby perform the intermediate transfer. The voltage can be applied while minimizing friction with the body, and the life of the intermediate transfer body can be extended.
[0136]
According to the invention described in claim 15, the charge elimination in the intermediate transfer member is performed by using a configuration in which a voltage is applied to the conductive saw-tooth discharge needle, so that the configuration is simplified and the length of the intermediate transfer member is reduced. Life can be extended.
[0137]
According to the sixteenth aspect of the present invention, since the charge elimination in the intermediate transfer member is executed by using the configuration in which the charge is removed by contacting the intermediate transfer member, the amount of ozone generated by the discharge can be reduced, and Environmental safety can be improved.
[0138]
According to the seventeenth aspect of the present invention, since the charge elimination in the intermediate transfer member is executed by using a configuration in which the charge elimination is performed in a non-contact state with the intermediate transfer member, a decrease in the charging performance due to dirt can be suppressed, and the reliability is high. The static elimination function can be obtained for a long time.
[0139]
According to the eighteenth aspect of the present invention, since the charge elimination in the intermediate transfer member is executed after the secondary transfer process using the intermediate transfer member and before the primary transfer process, the charge is eliminated at the most effective position. And the static elimination efficiency can be improved.
[0140]
According to the nineteenth aspect, the surface potential of the intermediate transfer member is controlled by using a conductive member capable of applying a voltage from the back side upstream of a position facing the latent image carrier in the moving direction of the intermediate transfer member. Therefore, the surface potential can be set to a predetermined condition while avoiding contact with the transfer surface of the intermediate transfer member, and a state where pre-transfer causing toner dust can be prevented can be achieved.
[0141]
According to the invention of claims 20 to 23, the conductive member used for controlling the surface potential of the intermediate transfer member can be selected according to the installation conditions and environmental conditions, so that the voltage application efficiency in controlling the surface potential can be reduced. It is possible to set a surface potential that can prevent the occurrence of pre-transfer in a good state.
[0142]
According to the invention described in claim 24, by performing the surface potential control by the charging method, even if the intermediate transfer body adopts a configuration such as a drum in which the voltage application for the surface potential control is difficult to be performed from the back surface, It is possible to prevent the occurrence of pre-transfer by controlling the surface potential.
[0143]
According to the twenty-fifth aspect, since the scorotron method is used as the charging structure for controlling the surface potential, the predetermined potential can be easily set using the existing established method.
[0144]
According to the twenty-sixth aspect of the present invention, the structure for applying a voltage by using a conductive member that can move at a constant speed in contact with the intermediate transfer body is used as a charging structure of the intermediate transfer body. It is possible to set a surface potential that suppresses pre-transfer while preventing generation of products.
[0145]
According to the twenty-seventh aspect, since the voltage is applied to the intermediate transfer member by using a conductive member that is not in contact with the intermediate transfer member, an image carried on the intermediate transfer member is provided. This makes it possible to set a surface potential that can prevent pre-transfer causing image quality degradation without being disturbed by contact with the image.
[0146]
According to the twenty-eighth aspect, the surface potential of the intermediate transfer member is set in accordance with the information of the image formed on the latent image carrier. By setting appropriate conditions, it is possible to reliably prevent reverse transfer.
[0147]
According to the twenty-ninth aspect, the transfer bias applied to the intermediate transfer member is set in accordance with the information of the image formed on the latent image carrier, so that the reverse transfer is optimized by optimizing the transfer bias. It is possible to prevent it with high accuracy and minimize the energy loss for preventing reverse transfer.
[0148]
According to the thirty-first aspect, since the toner used for forming the transferred toner image has a circularity of 0.94 or more, the reverse transfer can be suppressed with high accuracy, and the high image quality can be obtained. Can be further improved.
[0149]
According to the thirty-first aspect, since both reverse transfer and pre-transfer can be prevented, it is possible to achieve high image quality without image quality deterioration.
[0150]
According to the invention of claim 32, corresponding to each latent image carrier, a developing means for visualizing the electrostatic latent image on the latent image carrier as a toner image, and after the transfer to the intermediate transfer member, Cleaning means for removing and collecting the residual toner is provided, and for at least one of the latent image carriers, the developing means corresponding to the latent image carrier with the toner collected by the cleaning means; Since the toner recycling means for returning to the means is provided, reduction of waste toner can contribute to suppression of wasteful toner consumption and reduction of environmental load.
[Brief description of the drawings]
FIG. 1 is a schematic front view of a color copying machine as an image forming apparatus to which an image forming method according to an embodiment of the present invention is applied.
FIG. 2 is an enlarged view of an image forming unit and an intermediate transfer member.
FIG. 3 is a graph of an experimental result showing a relationship between a surface potential difference between an image portion and a non-image portion of a photoconductor and a reverse transfer amount.
FIG. 4 is a graph of an experimental result showing a relationship between a non-image portion potential of a photosensitive member and dot dust.
FIG. 5 is a graph of an experimental result showing a relationship between dot dust in an indirect bias application transfer method using a medium resistance belt and an indirect bias application transfer method using a high resistance belt.
FIG. 6 is a diagram illustrating a difference in a contact area between a toner and a photoconductor due to a difference in circularity.
FIG. 7 is a diagram illustrating a contact state between a toner and a photoconductor via an additive.
FIG. 8 is a diagram showing one of the configurations used in the charge removal process of the intermediate transfer member shown in FIG.
9 is a diagram showing another configuration used in the charge removal process of the intermediate transfer member shown in FIG. 2;
FIG. 10 is a diagram illustrating another configuration used in the charge removal process of the intermediate transfer member illustrated in FIG. 2;
11 is a diagram showing still another configuration used in the charge removal process of the intermediate transfer member shown in FIG. 2;
FIG. 12 is a schematic diagram for explaining a mechanism of toner dust generation which is a premise of the image forming method according to the embodiment of the present invention.
FIG. 13 is a schematic diagram showing a change state of a surface potential in an intermediate transfer member for explaining a pre-transfer prevention principle used in an image forming method according to an embodiment of the present invention.
FIG. 14 is a schematic diagram for explaining a pre-transfer prevention mechanism based on the principle shown in FIG.
FIG. 15 is a schematic diagram showing one of the charging structures of the intermediate transfer member shown in FIG.
FIG. 16 is a schematic diagram showing another example of the charging structure of the intermediate transfer member shown in FIG.
FIG. 17 is a schematic view showing another example of the charging structure of the intermediate transfer member shown in FIG.
FIG. 18 is a view for explaining another example of the image forming apparatus to which the image forming method according to the embodiment of the present invention is applied.
FIG. 19 is a diagram showing a state of occurrence of pre-transfer.
FIG. 20 is a diagram illustrating a difference in a state of occurrence of pre-transfer when a surface potential difference between an image portion and a non-image portion of the photoconductor is large and small.
[Explanation of symbols]
10,426 Intermediate transfer member
17. Intermediate transfer member cleaning device as cleaning means
22 Secondary transfer device as secondary transfer means
40Y, 40C, 40M, 40Bk, 402 Photoconductor as latent image carrier
61Y, 61C, 60M, 60Bk Developing Device as Developing Means
62 Primary Transfer Roller as Primary Transfer Means
80 Toner recycling means
101C, 101M, 101Bk, 425 latent image carrier static elimination means
454 Secondary transfer roller as secondary transfer means
150 Blade as one of counter bias means for controlling surface potential
150 'Roller which is another one of the counter bias means for controlling the surface potential
151, 151A, 151B Charging means
S Sheet as recording medium

Claims (32)

A primary transfer step of temporarily transferring the toner image formed on the latent image carrier to the intermediate transfer body, and a secondary transfer step of transferring the toner image transferred to the intermediate transfer body by the primary transfer to a recording medium. When the toner image is superimposed and transferred onto the intermediate transfer body by combining the above, an image forming method capable of collectively transferring the superimposed transferred toner image onto the recording medium by a secondary transfer process,
A step of removing the surface potential of the latent image carrier before executing the primary transfer step of the toner image to the intermediate transfer body; and a step of contacting the intermediate transfer body and the latent image carrier with the primary transfer step. Controlling the surface potential of the intermediate transfer member so that the toner on the latent image carrier does not transfer to the intermediate transfer member side before the step is performed. The image forming method according to claim 1,
The image forming method according to claim 1, wherein the intermediate transfer body has a rear surface area resistivity set to 10 ⁹ [Ω / □] or more. The image forming method according to claim 1,
An image forming method, wherein the intermediate transfer body has a volume resistivity set to 10 ¹³ [Ωcm] or more. The image forming method according to claim 1,
An image forming method, wherein a potential difference between an image portion and a non-image portion after the charge removal process of the latent image carrier is performed and before the primary transfer process is set within a range from 0 [V] to 200 [V]. The image forming method according to claim 1, wherein
An image forming method, wherein light irradiation is used in the charge removal step. The image forming method according to claim 1, wherein
An image forming method, characterized in that ions generated by an ion generator are used in the neutralization step. The image forming method according to claim 1, wherein
The image forming method according to claim 1, wherein the execution position of the charge removal step is a position corresponding to a position after the development step for the latent image carrier and before the primary transfer step. The image forming method according to claim 1, wherein
The image forming method according to claim 1, wherein in the charge removal step, a charge removal amount is set according to information of an image formed on the latent image carrier. The image forming method according to claim 1, wherein
The image forming method according to claim 1, wherein the discharging step is performed before transferring the second and subsequent color toner images when the toner image is superimposed on the intermediate transfer member. The image forming method according to any one of claims 1 to 9,
The image forming method according to claim 1, wherein the discharging step can be set for the intermediate transfer body separately from the latent image carrier, and the charge accumulated in the intermediate transfer body is discharged. The image forming method according to claim 10,
An image forming method, wherein a corotron-type charge eliminating structure is used in the charge eliminating step for the intermediate transfer member. The image forming method according to claim 10,
An image forming method, characterized in that a configuration for applying a voltage to a conductive brush is used in the neutralization process for the intermediate transfer body. The image forming method according to claim 10,
An image forming method, wherein a voltage is applied to a conductive blade during the charge removal process for the intermediate transfer member. The image forming method according to claim 10,
The image forming method according to claim 1, wherein a voltage is applied to a conductive roller during the charge removal process for the intermediate transfer member. The image forming method according to claim 10,
An image forming method, wherein a voltage is applied to a conductive saw-toothed discharge needle during the charge removal process for the intermediate transfer member. The image forming method according to any one of claims 10 to 15,
An image forming method, wherein a member used for neutralization is used in contact with the intermediate transfer body in the neutralization process for the intermediate transfer body. The image forming method according to any one of claims 10 to 15,
The image forming method according to claim 1, wherein in the charge removal process for the intermediate transfer body, a member used for charge removal is used in a state of not contacting the intermediate transfer body. The image forming method according to any one of claims 10 to 17,
The image forming method according to claim 1, wherein the discharging step for the intermediate transfer body is performed after the secondary transfer step and before the primary transfer step. A primary transfer step of temporarily transferring the toner image formed on the latent image carrier to the intermediate transfer body, and a secondary transfer step of transferring the toner image transferred to the intermediate transfer body by the primary transfer to a recording medium. When the toner image is superimposed and transferred onto the intermediate transfer body by combining the above, an image forming method capable of collectively transferring the superimposed transferred toner image onto the recording medium by a secondary transfer process,
A step of removing the surface potential of the latent image carrier before executing the primary transfer step of the toner image to the intermediate transfer body; and a step of contacting the intermediate transfer body and the latent image carrier with the primary transfer step. The surface potential of the intermediate transfer member in a state where the toner on the latent image carrier does not transfer to the intermediate transfer member side before is executed, with the same polarity as the toner carried on the latent image carrier, In addition, an image forming method is characterized in that surface potential control for setting the absolute value to be equal to or higher than the toner charging potential is executed. The image forming method according to claim 19,
In the surface potential control, a conductive member provided in contact with the back surface of the intermediate transfer member upstream of the facing position in a direction in which the intermediate transfer member moves toward the position facing the latent image carrier. Wherein a voltage is applied to the conductive member. The image forming method according to claim 20,
An image forming method, wherein a roller is used as the conductive member. The image forming method according to claim 20,
An image forming method, wherein a blade member is used as the conductive member. The image forming method according to claim 20,
An image forming method, wherein a brush is used as the conductive member. The image forming method according to claim 19,
The image forming method according to claim 1, wherein the surface potential control is performed by charging a surface of the intermediate transfer member facing the latent image carrier. The image forming method according to claim 24,
An image forming method, wherein a scorotron charging structure is used as the charging structure of the intermediate transfer member. The image forming method according to claim 24,
As the charging structure of the intermediate transfer body, a conductive member that can contact the intermediate transfer body and can move at a speed equal to the moving speed of the intermediate transfer body is used, and a voltage is applied to the conductive member. An image forming method characterized in that: The image forming method according to claim 24,
An image forming method, wherein a conductive member that is not in contact with the intermediate transfer body is used as a charging structure of the intermediate transfer body, and a voltage is applied to the non-contacted conductive member. The image forming method according to claim 1 or any one of claims 19 to 27,
An image forming method, wherein the surface potential of the intermediate transfer member is set according to information of an image formed on the latent image carrier. In the image forming method according to any one of 1 to 3 or 19 to 28,
An image forming method, wherein the transfer bias for the intermediate transfer member is set according to information of an image formed on the latent image carrier. The image forming method according to any one of claims 1 to 29,
An image forming method, wherein the degree of circularity is set to 0.94 or more as toner used for forming a toner image to be transferred. An image forming apparatus using the image forming method according to any one of claims 1 to 30. The image forming apparatus according to claim 31,
A plurality of latent image carriers, a latent image forming means provided for each of the latent image carriers, and a developing process for processing an electrostatic latent image formed on the latent image carrier by the latent image carrier into a visible image Means for transferring a toner image converted to a visible image by the developing means onto the same transfer member, and cleaning means for collecting toner remaining on the latent image carrier due to non-transfer. An image forming apparatus wherein the toner collected by the means is returned to the developing means and reused.

Images